How do I not pay the GC for repairs that were unauthorized

I hired a GC and we had a set agreement for for items, I left them in house that was empty to complete the work, after work I would stop by and inspect the repairs, which were painting, cabinets and sink tops and two toilets. I started noticing that other things were happening behind my back, like he painted all of the doors, not agreed upon, painted the garage after I told him that I was doing it and he used my paint to paint the doors, painted the ceilings etc. at the end he ask for more money and it was a lot. I told him I was not paying him for items that he chose to do on his own, and of course here we go. So I agreed to pay half to balance and for him to take a loss due to him completing items that were not agreed upon. So know I have at another house , this time I put it all in writing three items approved and a list of a few maintenance items that I asked for prices only, and he did it again. This time I am holding my ground and only paying for the items listed in my text message. I mentioned to him that he was stealing from me and forcing my hand to pay him on things that he chose to do. Dang I am stuck but before I pay him I wanted a wavier to protect myself and not sure which to used. Thanks Diane