More time posting than coding
First of all, sit down, relax, get a nice cup of tea and start reading. The search facility on here is your friend and a search on Winchester will bring lots of hits. Focus on the threads in HMRC Enquiries. There are lots of them and you've just started another.
THL are representatives of the same lot that sold you Winchester in the first place. Are you happy to give them more money? If so fire away. There are plenty of threads and opinions on THL, check them out. Do you know exactly who you would be giving your money to? Do you know what you are getting for it? Would you be getting value for your money?
If you need professional advice but can't afford it, there's an alternative. A collective group known as Big Group has formed via a firm of advisors called WTT. Their main man webberg posts on here. You may be able to join up with them and the shared costs may be within your budget.
If you want to do it on your own, ask yourself whether its wise to place reliance on anonymous contributors to a web forum which is known to be infiltrated with HMRC staff
and workers from the various schemes.
Webberg and another advisor Phil Manley (from the firm DSW) both frequent these pages and offer a free initial consultation. Doubtless other advisors are here too and may offer the same.
Good luck.