2001 530i problems - Saga

This car only has 49600 miles on it. Advice please! I'm at my witts end here. About 10 days ago the car just refused to start. The car was trailered to the dealership. They said the fuel pump was bad and put in a new one (OEM) for $600. Got the car back drove it less than 200 miles and the "Service Engine Soon" light came on over the weekend. Took it back on Monday, they called and said the fuel filter needed to be replaced. I asked him why they didn't catch that the first time and he said there were no fault codes for it. He said it could be bad gas. I told him I only put Phillips 66 premium in it and none of the other cars have problems. Anyway got it back yesterday (another $220 poorer) and it stalled on the way home from the dealership and refused to start again. Before it died it felt like it like it wouldn't accellerate. I could definitely tell it was going down. Called the dealership (not so nice this time) and he mentioned the "bad gas" theory again. They sent a tow truck to take it back. They haven't called today to tell me anything but I'm starting to feel taken advantage of here. Any ideas what this could be? Are they just causing more problems and charging me for their mistakes? I'm a single female so I don't really know much about cars so it's hard to argue with them. I've spent over $800 and they aren't done with me yet!
Thanks,
Liz