Seat belts won't retract sometimes won't let out.

you may have to remove the seat to gain access to the belt housing. inside there is a roller that spindles the belt to retract. they are easy to replace. i would advise going to a junk yard to get one that still works and use it. they are sometimes expensive. should just have a few bolts to remove the bracket from the floor and then one or two bolts from the top bracket.

pull it full out then let it go back in .if will not work change it.

Get a new one or a use one and repalce it your self

possibly there is something stuck in the belt not letting it retract

You did not state the age of your vehicle, however over the years, a seat belt will collect body oils, dirt, food particles, etc.
Pull your seat belt out as far as you can. Clamping in place makes the next part easier.
Grab a bucket of water, laundry detergent and a white (because you can observe soil staining) wash rag, then scrub your seat belt. Keep rinsing your wash rag and scrubbing the belt. Once the rag is no longer picking up stains, you're done.
Allow the belt to dry completely before allowing to retract.
Once dry, it should retract properly.
Do NOT lubricate the belt with silicone or WD40, etc. These are not designed for a safety critical item and are not required once the belt is clean.

Are you trying to say the seat belt retractor is stuck? This is in the front seat?
If it's anything like my Tahoe, you need to remove the plastic panel that covers the retractor (carefully - don't break the clips or you won't be able to put it back on). Take a large flat head screwdriver and slide it under the part where the seat belt coils up, and find a little tab - push it with the screwdriver. As long as the seat belt is not twisted up, it should retract.

have a look to see if its coiled in twisted as you pull the belt out if the buckle doesn't line straight to the female end well its probely retracted in twisted to repair pull the belt out all the way and then realign the belt its quite hard to do so take your time hope this helps.

Take a good look at the seat belt make sure its not twisted or something has fallen in the retract,you may need to pull belt out and try to keep lightly pull to see if it retracts, if not then you will need to replace, sometimes they just get stuck but if you work it for a while pull belt it may retract it is just stuck,

You may have something in the retracter for the seat belt so you will have to acces it and take a look to see what is in there.

The mechanism that allows it to retract is broken. Replace the seat belt.