Sorry but won't I need to sign the policy or tick the necessary box for purchasing the PPI?

Thank you

Hi i am new in this forum. I just need some advice. I have missold PPI by Capital One and have been paying for 7 years I realise. I I filled a complain form and sent to them. They replied my letter in 8 weeks and told me that I haven't missold PPI . They say that If I would like them to review my case again, I have to write them with relevant details. I am not going to write all thing they told me but I just need some advice from you. In their respond they told me that when I applied to Capital One Credit account by completing a postal application on 18 June 2004. and at that point I did not indicate that I wanted to purchase optional PPI and as a result it was not applied to my account at that stage. But I purchased the policy during a telephone conversation on 11 February 2005. they phone me and I purchased the PPi on the phone. Are they allowed to do that? because I did not sign any policy agreement. Thank you