Miway stop *****ing my money

I had a policy with Miway and had agreed on a premium if about R300+ per month. Out of the blue they increased the premium to R887.37 without consulting with me. I then cancelled the policy with them after I did not get any joy from the company. They gave been debiting my account the sum of R887.37 for the past 4 months despite the fact that I cancelled the policy with them 5 months ago