Non-existent service

MBD bought over an old ABSA/Virgin debt of mine, which I had been paying off all along via my PDA. It was paid off early 2021. They wouldn't give me a Paid Up letter, saying I still owed an amount. There was no getting through to them, so I added that account back onto my monthly PDA payments, and paid that off. So that's a 2nd time paying it down to zero. MBD still don't want to give me a Paid Up letter, despite me sending them 12 separate emails showing proof of payments made by the PDA into that account. All the while, MBD harass me with daily phonecalls (up to 7 a day), multiple different agents, each not knowing anything about the matter that Queries Dept is handling, for the last 2 months. Still no response, and no Paid Up letter. This is pathetic, non-existent service. I'm not paying this debt off a third time. In fact, I should not have paid it off a second time. How difficult is it to get a statement from the account??