It has to be something so at this stage I feel it would be wrong to make any assumption. At the beginning I would not have expected there to be a problem with that combination and there may well not be but all things have to be considered in view of what has happened.
I really doubt that this is going to work from this position and I think it would be a waste of time just waiting any longer. If it were me I would make a 100% water change without using prime. Then add a single dose of biomature and test the water for ammonia and see if that one dose is converted to nitrite and then nitrate without adding a second dose.
No not really, there is very little chlorine actually gets through the system to the tap. Lots of well known breeders and fishkeepers never even dechlorinate. I always do as a precaution but there is little point in repeating the same thing which has just failed and because the ammonia seems so stable there doesn't appear to be that much of a bacterial colony present anyway. So its worth the risk.