I'm sorry you're having such a hard time with this.

I would call the other shop and tell them the *WHOLE* story, how many times you've been in etc, etc. Tell them you want a fitting but you don't really feel like you should have to pay for one since you just bought the bike from this other store. I don't know if they will give you a fitting without additional cost. But they might reduce the rate.

I do bike fitting and I am repeatedly surprised by stories like this. It's ridiculous. There is definitely more that can be done with your fit. A good fitter will find the best position for your body and won't just to a fit by the numbers (which is really sizing as you've mentioned). And, a good fitter will be able to tell if your problem is related to the bike fit or more related to your own muscular limitations (which doesn't sound like a problem for you).