Rear Seat Belt problems of the 2001 Mitsubishi Mirage

My rear middle seat belt did not function so when I went to get my safety check from Mitsubishi hawaii they charged me to replace it, stating they could not complete my safety check since the seat belt was not functioning. At the time of service, my 5 year manufacturers warranty had expired by one week. When I took my car to another service company to get a tune-up (that Mitsubishi said I needed even though I just had one six months prior), they told me it was illegal for the dealer to charge me to replace my passenger restraint system that was dealer issued and faulty. I called Mitsubishi and they said they had never heard of this law and that I was charged because my warranty expired by a week. No one bothered to consider it took two weeks to get an appt and my warranty was in effect when I requested the appt. This charge does not seem fair since my warranty expired on Feb 22, 2006 and the earliest appt I could get was on Mar 1, 2006.