Not receiving my subscriptions

I have not been receiving my Cake Decorating issues. the last issue I received was November. Debit orders continue to go off and I just don't get anything. I have tried cancelling my debit order with them, complained with them in not receiving my issues anymore. demanding my monies back and they keep on telling me to tell them which ones I have. so I told them which ones I think I received but I don't keep record of what I receive from them as some issues prior to registering with them have been bought in shops like CNA or Spar. and now they don't want to reimburse me as I cant prove what I have received from them. I asked them to check there records as they will be able to see what was collected at the Postal Services and what I signed for. How can I resolved this to get my money back and for them to cancel my registration with them.