Rear Seat Belt problems of the 2005 Chevrolet Tahoe

We own a 2005 chevy trail blazer. Our 11-year old son fell asleep and lay down with shoulder-harnessed seat belt on in the back seat - passenger side. Upon arriving at our destination he was awakened. At this point he sat up, released the latch, an tried to get out. The seat belt was twisted around his waist and as he tried to untangle the belt the ratchet got significantly tighter. When I realized the problem developing and got around to him the belt was so tight that I could not untangle him or slip him through the loop. He was in severe pain. He had either turned in his seat, or sat up on the wrong side of the shoulder strap, or something else. Not wanting any injury to my son's back or any internal organs I had to cut the belt. It was about 12:30 am. I have since been told that for shoulder harnessed belts, when the shoulder strap is pulled all the way out as for use with child safety seats this engages the ratcheting mechanism. I believe that there needs to be a "release button" for emergency use on the back of the column which houses the shoulder strap. Since the brakes were not engaged I did not understand why the shoulder strap would not loosen.