Contract cancelled but I'm still getting billed monthly!!!!!!

I signed up for a rain simcard in October 2020, I noticed from the moment the sim was activated that the network coverage was extremely poor. I had opted for the unlimited package and was utterly disappointed to say the least. I made countless contact with their support team to resolve my network issue and they told me that the wasn't any coverage in my area. Eventually I canceled my contract with them on the 5th of February 2021. I saw on their page that they would debit me for the data I used during the month of Feb, I got debited a full months worth of subscription today and I don't understand how or why because I didnt even use the simcard from the 5th. I tried to get my bill, that shows my usage and it was nowhere to be found on their website. I checked again when their next debit will be and it showed that I will debited again on the 1st of April 2020 and I won't lie I'm livid. I long cancelled this useless contract, yet I'm still getting ****med by this company. I want my money back, and I also want something in writing that shows that my contract has been cancelled. I know my consumer rights and I know exactly what I signed up for, I will not accept this nonsense from RAIN.