Rear Seat Belt problems of the 1998 Nissan Altima

In March 2001, I had my child in a car seat buckled in the back middle seat. When I went to get her out of her car seat when we stopped the lap belt was broke. I had it replaced in April and the same thing happened. I went to the dealership for a different kind of seat belt and they said all they can do is order the same one they replaced that broke which I don't want because it isn't safe it can't hold a 30 lb. Kid. When I called 1-800-nissan1 the lady on the phone told me that it isn't meant for car seats it puts too much of a strain on the seat belt causing it to break. I called the highway patrol because that is wear they install it and they said under no circumstances should a seat belt break. It is also in the car manual to install the car seat in the middle of the back seat as well. I am lucky that I wasn't involved in an accident that may have severly injured or killed my daughter. I think the public should be aware of this problem.