Tried to rip off my girlfriend

I was at work when I got a call from my girlfriend telling me that the car was broken. She said it was really loud and something was dragging (muffler) and I told her not to worry because we had just had the muffler and straight pipe replaced 6 months earlier (in Ottawa for $350/new parts). She took it to Crosstown and spoke to FRANK who said not to worry because the part was still under warranty. He told her with the parts under warranty it would be $940 and that she needed to do it right away. She called me I went through the roof with anger and told her to park it and I would take care of it. I asked her to get a paper copy of the estimate and FRANK was unable to provide one. I spoke up, and told him I needed one before I could okay the repair. He said I would have to come back.
I took to J & M auto in Ottawa and they fixed the muffler and a ball joint for $285.