There's no easy way.
Incapacitated doesn't mean helpless, or that a creature's defenses are down.
Incapacitated creatures are aware of what's happening around them, can move normally and interact with objects, and can oppose attempts to move, grapple or disarm them.
Grabbing an incapacitated creature still requires a Strength(Athletics) check opposed by the creature's Strength(Athletics) or Dexterity(Acrobatics). Depriving them of something they are holding would also be resisted by their Strength(Athletics).
Incapacitated creatures aren't especially vulnerable to intimidation, persuasion, or anything else. Their AC isn't lowered. And so on.
The Hypnotic Gaze feature, however, has the specific additional effect of also charming the affected creature; that means that some interpersonal interactions can be attempted (by the enchanting enchanter) with advantage. But that also wears off as soon as any damage is dealt.
There is no official ruling, but allowing it does not seem to be unbalanced.
As you mentioned in your question, there are no explicit rules stating how the Net interacts with being Oversized (made for something larger than Medium), and I cannot find any official statements from Sage Advice addressing it. Therefore, this is purely up to the DM.
But, for the sake of looking into this a little more closely...
Prior Edition Precedent
Per the 3.5E SRD:
A net is useful only against creatures within one size category of you.
So, in 3.5E, if you were a Medium creature, then a Net sized for your use would work on Small, Medium, and Large creatures, and nothing else. Therefore, if you were Large and using a net made for a Large creature's use, then it would work on Medium, Large, and Huge creatures. So, per the 3.5E rules, an oversized net (made for a Large creature) would work on a Huge creature.
So, there is established D&D precedent for a Net targeting different sized creatures based on the size wielder it is made for.
Thematic Analysis
While there is no explicit statement saying this, logically it follows that the 3.5E ruling works for this reason: too small of a creature would fit through the gaps of the net and not be restrained, while the net wouldn't be big enough to entangle a creature that was too large (you might wrap it around one leg...but that's not going to accomplish much).
Mechanical Analysis
A weapon that can apply the Restrained status is certainly useful. Restrained is a fairly nasty condition. However, a net is quite easy to get out of...for most creatures, it just eats up an attack or an action, and there are lots of things that do that.
Additionally, if we take a look at Grappling...
The target of your grapple must be no more than one size larger than you and must be within your reach.
So, a Medium Creature cannot grapple a Huge creature, same as they can't hit them with a Net. But an Large Creature can grapple a Huge creature. So, even within 5E, there's precedent for player-applied conditions that only work on certain size creatures scaling with your size.
Conclusion
Based on the 3.5E Precedent, and the way Grappling already behaves, I see no reason why this would be unbalanced, and it makes sense from a thematic perspective. If you are still uncertain and want to add a drawback to this, then adopt the downside provided in 3.5E: As you increase the size of the net, it stops being able to restrain creatures that are too small.
Best Answer
It was legal, since there was no effect stacking
The Restrained description says:
None of these effects stack (I mean disadvantage and zero speed), but you didn't want to stack them. You didn't want to restrain the target more. You said you used another net to make the target waste two actions:
A creature can attack the net, or win the STR contest to set itself free. But is not an effect, it is a possibility to get rid of the net. If you want to cut two different nets, you have to attack at least two times, the same with the STR contest. In this sense, multiple nets can "stack" indeed.
The DM might say otherwise
Results of the STR contest depends on the DM ruling though. He/she might say a creature can break itself free with a single burst (with a higher DC for the STR check, maybe). The details is up to the DM.