AC Leak after transmission was replaced / Rebuilt auto transmission shifts more abruptly than before

I recently had my auto transmission replaced. It worked fine for a few days,then started shifting itself in a bizarre fashion. I brought it back and when i got it back,the air conditioning was barely working. Now, they say I have a leak in the system, but they are having a hard time finding it. Also they say that the air conditioning going bad right after replacing the transmission is just a coincidence, and I'm responsible for any costs relating to its repair. What could have happened during the replacement of the transmission that could have caused this?The transmission now shifts differently, more abruptly than it used to.When you let off the gas while accelerating, it drops down a gear more abruptly than it used to.