Motor mile / bpo collections help

A few months ago I kept receiving voicemail messages from Motor Mile claiming I owed them money, I rang them back and explained I dont..they said it was from a payday loan back in 2011, again I stated I have already paid this bill with Quick Quid back in 2012. They kept ringing me so I just started to ignore them, and now today I have recieved a letter from a company called BPO Collections claiming I now owe them an outstanding balance of £165.24, they dont tell me what the debt is for only that they were instructed by Motor Mile to collect the remaining balance, I dont know what to do. ive already told Motor mile I have paid the bill and all they said was 'there is no proof' I ever have, its stressing me out. Please help!