Didn't you have a walk thru of the house? Didn't you get proof of the repaired item before closing or at closing? I am buying my first home this month and I have a walk thru scheduled as well as have demanded receipts and reports on all repairs fixed, etc.
Where is your Mom? I am so sorry that your Mom would do this to you. If you are a co-signer for anything, the other person's name appears on all the documents as well. That's how you know if you are the sole signer or not. If you cannot work with your Mom to get the car back ASAP, report it...