So I went to Greg's Auto repair for a check engine light. It came up that both cats were bad, bank 1 and bank 2. He charged $70 to diagnose for me. I brought my car to audi because my car is under 80 thousand miles, and they are telling me that I still have to pay the $112 to diagnose the problem, whether the cats are bad or not. I wasnt happy about this but they kinda had me by the *****. So after about half an hour the service rep comes to me and tells me both cats are showing trouble codes so I need an update for my ECU, thats gonna cost $180 total. Now I'm tight as a tiger, but I still cant do anything else so I have them do this update. 5 hours later the check engine light is back on and I'm out $180. Now they say they will replace both but the part has been on back order for two weeks. I guess this first part was just me venting. My real question is does my cats being bad have any effect on the terrible gas mileage that I am receiving? Also has anyone gotten their $180 back from Audi after the cel has come back on?

Thank you