In the first example, "number X" is modifying the subject "order" as part of a series. The "1" and "2" represent the place in the series:
I need RMAs for orders number 1 and number 2 (out of 5).
I need RMAs for orders 1 and 2.
I need RMAs for orders number 1 (ID# 56789) and number 2 (ID#56790).
Making "numbers" plural instead indicates that "order numbers" is the complete, more descriptive subject, similar to "tracking numbers" or "inventory numbers." That ties it directly to that item, no matter how many orders there are or in what sequence. This makes more sense if for example you provide a complete tracking number:
I need RMAs for order numbers 1234-XYZ-0987 and 1234-ABC-7890.
Of course this could also be shortened to just use "orders," which in that case is the complete subject & needs to be plural.
I need RMAs for orders 1234-XYZ-0987 and 1234-ABC-7890.
By most modern understandings, have to and must imply compulsion, should implies obligation without compulsion, and shall implies firm intention or commitment - or is just used in place of will to lend a certain air to the text or speech.
In contracts, standard documentation and various other specialised usages have their own understandings of the term. If you need to understand them legally, you should speak to a lawyer. I know in some cases shall is a stronger term than must, and in others it is the only acceptable thing because the document is describing what each party is committing to do.
To reflect "internal necessity or inner passion", I would say that you are talking about a compulsion, so "have to" or "must" are both appropriate. They are both (effective) modal verbs, and as such can theoretically be used in any tense, though not all modals exist properly in all tenses; "must" is often replaced with "had to" to express compulsion in the past or with "have to" to express compulsion in the future. They are also both used in front of the have of the perfect tense in order to indicate inference in the past, just to be clear.
I have to park there.
I must park there.
You have no choice but to park there, or are under some strong compulsion to do so. This is often used in a hyperbolic manner, to express a strong need or desire to park there (or whatever the verb is), without there being literal compulsion.
I had to park there.
This means you had no choice but to park there.
I have to have parked there.
I must have parked there.
This means that you may not remember that you parked there, but all the evidence suggests that you did park there.
I had to have parked there.
You may not remember that you had parked there some time in the past, but the evidence suggests that you did.
Using them about the future restricts you to have to rather than must, unless you use the futurate (the use of the present tense to talk about the future).
I will have to go to school tomorrow.
That's the future tense with the obligation/compulsion.
I have to go to school tomorrow.
I must go to school tomorrow.
That's the futurate.
Best Answer
They are both "correct". They just have a difference of nuance.
I must have dialled the wrong number implies that you didn't think you had, but obviously you "must have" done so because the person you wanted wasn't there. It's an expression of surprise and a tacit protestation that you thought you were dialling the wrong number.
I have dialled the wrong number is just a statement of fact. It is saying that you dialled the wrong number, without really any nuance or anything. It might be used when you realise that you really did dial the wrong number, that you made a mistake (reading the wrong line of your address book, for instance).
However, the nuance changes when they are prefaced with I'm sorry. If the apology is a distinct clause, the original difference applies - you are saying that you are sorry, and that you (must) have dialled the wrong number.
Those would be more natural/usual, in my experience, than the alternative:
Because there is no separation of clauses, the "I (must) have dialled the wrong number" becomes a modifier of "I'm sorry", which would be taken as showing what you are sorry about. You not apologising and stating that you dialled the wrong number, you are apologising for dialling the wrong number. This is valid and 'correct', but not usual - at least not in terms of what you say to the person who picked up the phone.
Also, the have isn't necessary in the version without the must. The simple past works just as well. If you want to use the perfect, it would be usual in most dialects that I'm familiar with to contract the "I have" to I've.
So, use the comma after sorry and then use must or not depending on what you are trying to say or indicate.