Do I have to pay a PPI company when I win my own claim

[Stressylady]

I started my own PPI claim against a bank in 2015 that has been dragging on forever. In 2019 I signed up with a PPI company to see if I had any other PPI as I’ve had lots of mortgages, loans and credit cards. I did tell them I had started a claim with a bank already so they were aware of it. Obviously they located the said PPI on their search also and asked me to recomplete paperwork which I did thinking they may have more joy. The bank wrote to me to say they would close the new complaint down as they already had an existing claim with me. Then they finally resolved my claim and the PPI company promptly sent me an invoice saying their claim has been resolved?? I’ve told them the claim is my original one but they are asking me to prove it. I’ve sent a copy of my original claim letter and the questionnaire I submitted along with a copy of the letter saying the bank would stick with my original complaint but they aren’t having any of it. They say the original complaint is theirs even though it’s 4 years after mine and I must therefore pay it. I have written to the back asking for clarification of who’s claim they have paid but I’ve a feeling they aren’t going to go away even if the baink come back and confirm it’s my own claim. Does anyone have any advice please as these guys are relentless and the daily haranguing is making me ill ☹️