Same scenario, and I've told Arrow that just because the purchased the alleged debt, that doesn't given them rights in any commercial affair concerning me so pack it in.
ALSO, that MBNA, knowing that the matter is in dispute, are breaching certain industry regulations.
PLUS, the alleged debt is apparently part of an agreement (unsubstantiated, unenforceable) between myself and MBNA, but because Arrow weren't party to that agreement they have ZERO rights. AND the alleged agreement is between me and MBNA, I have contended that there is NO agreement between me and Arrow of any kind, and they have in fact paid an unenforceable debt off in my name, which in law is deemed as a gift and I'm under no obligation to repay as I was not party to their actions. BTW, that account is now deemed SATISFIED and CLOSED on my credit file.