Need Advice regarding debt collection agency

Hi I had a bank loan of €18k, I fell into financial trouble after a separation & I missed some payments. I communicated with the bank and explained my situation. They accidentally sent my loan onto Cabot financial! Which I was sent letters from the bank & Cabot financial to set up an agreement. I got in contact with the bank only to be told the loan was mistakenly transferred to Cabot financial debt collection agency if I decide to stay with the agency I can pay the loan back interest free of charge. That was fine so I agreed. But there’s been 2 occasions since then, that Cabot financial have closed my loan account and reopened a new loan account ! Ive gotten 2/3 letters from the bank since then to say they’ve closed down my loan account and also letters from Cabot welcoming me to them and new reference number. Very confused as to what’s going on. This is going on over 18 months now and I’ve already paid off around 4k since.. but the new accounts don’t have my payments history. What are my rights here ? I rang the company they’ve no clue what’s going on they just want their money. They told me I will continue to have bad credit for as long as I owe them money - I’m not refusing to pay I just want to know what’s going on. God knows what my credit score is like now I can’t imagine the damage that’s been done here, not even Klarna will accept me for a small purchases.

where do I go from here? What steps to take next? I’ve read so many bad reviews on this company!