Successful ppi claim

I signed up with a 3rd party to deal with my ppi claims back in april 18, progress was slow the company have been quite incompetent at times losing papers i signed etc etc and sending out new ones to then get lost again, phoning me for info when they have already been provided with it. Anyway i had 2 successful claims in which they claimed over 35% of my pay out, bit peeved but knew i signed up for it. Now we are in october 18 and one company contacted me to say that they were dealing with my claim direct as they had asked my 3rd party to provide the signed authority however they couldnt provide it, they said they had logged my claim and i would hear within 2 month, in the meantime i heard nothing from 3rd party, now the 3rd party send me out new forms for me to sign for them to send to the ppi company as they have lost the originals, they have in all honesty been a pain as they keep losing my stuff, now today i have received a final offer from the company with cheque, direct to me as the 3rd party have failed to send the info over, i have only just rec the new forms and now had the pay out, do i do the honest thing and pay the 3rd party the 35% although they did nothing in this case or do i ignore and keep all the money, please can i have some advise, just to confirm there is no signed authority as they lost the originals.