I was going through my bank statements recently when I came across a direct debit for the sum of £4.99

I phoned my bank and asked what this direct debit was they replied it had been going from the year 2000 and gave me the policy number and phone number of the insurers, when I phoned I was shocked to discover it was for a mobile phone that I had taken out with Dial a phone back in 2000 on I believe 12 month contract on behalf of my son, it has now materialised that the policy I thought was maybe pet insurance was for a mobile phone from nearly 9 years ago, when I spoke to the girl on the phone at the insurance company she told me it was my responsibility to cancel this where as I thought that like the phone this should have also been 12 month contract can anyone enlighten me as to where I stand in this fiasco please!!!!