HiCustomer my name is Mike.
Do you mean that it is locked in such a way that you cannot pull anymore length of belt out?
HelloCustomer I have included a link to some pictures of the Equinox I had in my bay today. This was a 2007 model but I am pretty sure it is the same. Although they may have added a piece to the webbing of the belt to keep this from happening. In the last photo you can see how far the seat will lift with the seat belt buckled so that you can access the release button. In the second photo you can see the excess slack because of the button added to the webbing. In the first you can see the button. If you do not have this button I can get you a number for a new one, the replacement is a little bigger but it will make sure this doesn't happen again. It looks alot like the one under the buckle on the webbing it is just placed higher up so that the belt doesn't sit tight.
On to your immediate issue. I found that if I buckled the belt and pushed down on the seat as in picture 2, I was able to slide my hand inbetween the seat and find the red release latch on the buckle. This is the only way I can figure out how you could get the seat up without taking the seat apart or even out of the vehicle all togeather.
CLICK HERE TO VIEW THE PICTURES
Oh my that is too bad. I think the only course of action for you is to take it to someone and have the seat taken apart.
Since that is the case I would strongly suggest getting a button like the one shown to prevent this from happening again. If you would like I can get the part number and a measurement for where to install it tomorrow.
I wish I could be of more help but once the belt is locked and the seat is not upright there is not a way of making it retract without leveling out the retractor assembly and that means either removing the seat or disassembling the back of it to get the retractor out.
One more thing are you sure you are out of warranty? How many miles are on your car? What is the delivery date? If you are under 34,000 miles and are unsure of the delivery date post the last 8 didgets of your vin and I can tell you.
It's not a problem I wish I could be of more help.
I ran your vin and it is not good news. Your warranty ran out on July 2, 2008 and you have no GM service contracts. Your last hope is if you have an aftermarket extended warranty. If not I am afraid you will have to pay for the repair.