Currys PC World

My daughter has been charged £6.50 per month for the past 3.5 years. It was shown as Product Support AG 0844 800 6080 and she had no idea what it was for. We found the free phone number and found out that it was Currys PC World. The agent said that it was for an HP laptop that she had bought. When I asked for proof that she agreed to pay this we were told that the paperwork was destroyed after 6 months when it is assumed that she was happy to pay. I always assumed that paperwork proving payments were to be made were kept for at least the duration of the policy. The agent was most unhelpful and I got the feeling that they were so used to complaints that they ignored them. The payment was not a direct debit, but a reoccuring charge to a debit card. This has now been cancelled by the bank. If the paperwork has been destroyed how do they know that it was for an HP laptop?