Seat belt stuck really stuck!

Hello thanks for adding me to the forum/club, and my first post is a request for help!

I have a issue on my 06 Zafira B, where the middle seatbelt is well and truly stuck, I have made sure the seat is back in the correct position and tried tilting the seat forward which only made it tighter, after a visit to Rowcliffes in Taunton on Wednesday they where unable to free it and quoted me £406.40 ( yes £406.40!) to replace the seat belt, told them no! Now to get the seat back in the upright position I have had to cut the seat belt, and it seems to work fine except for being cut off!

I seem to able to source a replacement easily on the interweb, how easy is it to replace the belt myself, assume I will have to take the seat out and the cover off to get to the mechanism, or do I just take the seat cover off, and how easy is it to get to the anchor point in the seat or is there an easy to follow guide anywhere

Thank in advance of any replies

Adrian