Sounds to me like they are giving you the run around. You need to find a shop with a good reputation. A corolla does not have seven 02 sensors. You should get the code from autozone first before going into a shop. Also research the code you receive along with “Technical Service Bulletin” your code will come in the form of the letter P followed by four numbers (P1234) So when googling this try many different ways such as “Toyota Corolla P1234” or “Toyota Corolla P1234 technical service bulletin.” This just might be a common problem with this car. Due to the popularity of this model, I own one myself, there has to be others with the same problem on a forum somewhere.