Q: Engine light on

Check engine light has been on. Took it to a neighborhood mechanic. He put the computer on it and the code came up as a bad O2 sensor. He told me he needed to change the O2 sensor. There was also a terrible squeaking in the back of my vehicle on the inside. It sounded like something was rubbing or jammed up against something in the back of the truck. After the mechanic drove with me for a short time he told me he was pretty sure I needed shocks. I dropped the car off and he change the O2 sensor and check the shocks telling me they were bad and he replace the shocks in the rear of my Escape. When I went to pick up the car he told me that the squeaking did not go away and it was still the same. It is the next day and I have a car that sounds identical to before when I brought it in and my check engine light is still on. He wants the car back today to take another look at it. I am upset that he told me this would be an easy fix and nothing seems to have gotten fixed. Please advise. Thank

My car has 86000 miles.
My car has an automatic transmission.