blames client for delay

I had a courtesy vehicle for 30 days and am eligible for extension, should it take longer to fix my car, now the car is not done and they want me to return the rental car to avis and my application for an extension was declined on the basis that parts were delayed hence the real problem is that they asked me to get a nbc letter from miway which in this case is my previous insurer so apparently miway gave them a tough time in trying to get the letter and I got it in 15min which was not my part to play, now they are complaining about parts and when I called the repairer they told me all is in place they just need time to complete the job and the longest period it would take is 7days including weekends to complete the work. now I must walk and I work till late and there is no public transport available at that time. so I won't be able to get to work until I get my car back.