Can't get boat back????

I'm in the state of South Carolina. Our boat messed up & had to be fixed. It is covered under a warranty w/ a $25 deductable. We were told that our boat was fixed & could be picked up. When we went to go & get it they told us that the "insurance/warranty" company not to them what they would cover & that we would have to pay the balance of $500.00 instead of the deductable before we could get it. My question is: Shouldn't the the place have checked coverage before doing work on our boat to make sure that it was covered & that we still wanted the work done? All of it should have been pre-approved first & wasn't. What can we do?