Hi Lucy
Firstly, when your dad cancelled with AOL, did he cancel over the 'phone or in writing? If it was over the 'phone, then did he get the name of the person he spoke to?
Secondly, if he set up a Direct Debit with them, then really he should've cancelled it straight away when he cancelled his contract with them.
Personally speaking, if I were you, I would have a look at the contract he received as I'm sure it would state on there regarding cancellation etc. I would also write to AOL detailing the exact turn of events and head it "Formal Complaint" and make sure that you explain in detail that your dad is a pensioner and would have not realised that he had to cancel the direct debit.
Having spent some time on the 'phone to AOL recently, I feel that in writing is your best course of action. I would also send your letter recorded delivery then you can check on the Royal Mail website that they received it and print off a proof of delivery.
Let us know how you get on
Bo
