Sun Auto made unecessary repairs trying to fix the problem and never did fix the problem or refund me my money Austin Texas

I took my auto to Sun Auto because my engine light was coming on for a couple of days then would go off for a couple of days before coming back on.Auto Zone read my codes and said i needed a catalitic converter.When i went to Sun Auto and explained how my auto was acting the store manager instantly told me it was not my catalitic converter because when a cat converter goes out its gone,no coming and going.The store manager said Auto Zone did not know  what they were talking.Auto Zone had also told me it could be carbon builb up in the intake manifold giving me a false reading.  

The store manager proceeded to tell me they would do a diagnostic check to see what the problem was.Since he did not think the problem was the cat converter he went looking elsewhere.He came back and once again told me it was not the cat converter because the engine light was coming and going.The store manager told me that the cat converter was too expensive to replace and have it not fix th problem.He told me he thought it would be best to replace the canister purge valve and evaporation control canister first to save me the expense of a new cat converter that in his opinion would not fix the problem.The total cost for the repairs was $627.49.Still pretty expensive if you ask me,especially for a senior citizen on a fixed income

Two days later my engine light came back on.I was told to bring it back in and they would look at it again,free of charge.this time i was told they would flash the computer and that should fix it,another $129.71.The auto was running worse than before.I called them again,told them my car was runing worse than before.Again i was told to come back in and they would look at it again,free of charge.this time i was told bt the store manager that it needed a cat converter.He gave me an estimate of$1397.85 for a new cat converter minus $757.20 for work done before that did not fix the problem i was having.still leaving me with a $640.65 bill to fix something he had told me did not need fixing,the engine light coming and going that he had said was not indicateing that the cat converter was bad. 

I called back a few days later and told the store manager that since the repairs they had done did not fix the problem,shouldnt i get a refund.He told me the parts were in the car and that he could not give me a refund.If i was willing to spend more money ther i guess he could see giving me credit for the money i had already wasted there.The store manager is a fast talker,makes it very difficult to understand what he is saying,kind of like  when a hustler or con man is trying to talk you into something.