As I said in the post you quoted,
So, if you don’t know how to find your remaining credit, you are going to have to ask your specific Service Provider how to do it - it has nothing to do with Wavecom or Open-AT.
See above - there is no standard way to do this, so there obviously can’t be an ADL API specifically to do it!
But, of course, you can handle AT Commands & responses with ADL…
If your specific Service Provider uses SMS, you can, of course, use the ADL SMS Service to do the same thing.