Learn English – was to be and was to have been

I think the primary source of your confusion is conflating three very similar uses of these words. “Break” and “down” can be combined in different ways in different grammatical functions to say different things.

“Breakdown” as one word is always a noun, specifically a catastrophic event that a car can have.

breakdown    noun

a failure of a machine to function : an occurrence in which a machine (such as a car) stops working
_{Source: Merriam-Webster definition of “breakdown”}

• My car had a breakdown.

“Break down” as two words is a phrasal verb, the first word of which can be conjugated to indicate the timeframe of when a breakdown occurred, e.g.:

• My car broke down near the circle around eight o’clock this morning.
• My car has broken down.

“Broken down” can also be an adjectival phrase that describes a car that has broken down, e.g.:

• My car was broken down until ten o’clock this morning.
• My car is broken down.

None of these options are particularly grammatical.

The most common versions would be to say:

I fasted today.

This is a simple statement of fact.

I was fasting today.

This implies that you were fasting but are not any more.

I had to fast today.

This says that something required that you fast today.

I have had to fast all day.

This says that you've been doing it for a while and can (but does not necessarily) imply that you are no longer doing this action.