Hi
Don't pay someone!!
I did the form myself and it was extremely easy - just sent one letter from the template on Money saving forum, sent it off and got an offer letter 3 months later. it took me about 20 minutes to do and that was that. No chasing up, no phone calls and even better...no fees! I still don't know if I'm going to get the refunded PPI though and I'd be careful about using a company simply because if for whatever reason you don't get the refund paid to you, you are still liable for the fees as it counts as a 'win'.
