Problems with PPI claims managenment companies

[Snodgrass]

I filled a form in in June this year for a claims management company to check if I had PPI. I heard nothing at all, the deadline came and went, so I assumed nothing had been done and I was prepared to leave it at that. However, I have just been contacted by them to say they have traced some PPI and want me to sign a further letter of authority for them to investigate further. However, I have since heard some worrying stories about claims management companies and do not wish to proceed further. if I don't proceed they say they will bill me for the work they have done so far but don't know how much that will be. Does anyone have some sage advice?