Assupol will not cancel debit order despite written request to cancel funeral policy

I have tried to have a funeral cover with Assupol Life but have found that as a pensioner with a pension fund that diminishes every year, I cannot afford it. I wrote to Assupol to cancel the policies. A response came after 3 months asking me to fill a cancellation form. It has been 2 months since I filled their form but the debit order still goes off. However, there is never enough money, which fact was communicated to them in writing. Assupol is not cancelling the debit order and this places me in a bad light with the bank, causing unnecessary penalties.