Incorrect billing-Why am I being billed when this sim was cancelled a month ago already?

This is my second request, no one cares to respond to customer queries which also explains why your billing system is so flawed because you have no interests in the customers. I cancelled my account in March. Now I'm receiving a message that my account is in arrears. How can my account be in arrears when I personally cancelled this sim card on the 2nd March. I received a Bill for February for services I didn't use and I paid this because I was given so many stories by your call centre and them telling me if this amount is not paid i won't be able to cancel he sim. I paid the amount even though I never used your services it was just so I could be able to cancel the sim. I won't do the same thing again for March. And hoping that you will resolve this mess before April becasue the more you delay the more this bill is piling up for a sim card i don't even own anymore.

I want feedback on this and you need to clear this amount in arrears as I don't owe you any cent! I haven't used this sim card since January 2020 but every month I'm being billed. I tried resolving this with your call centre and they told me the only way is to cancel my sim card so i don't get billed which I did. But now still even after cancelling my sim card I'm still being billed. It's totally unfair because I can't even log into this account to download my statement. I'm going to report this with the Ombudsman if no one gets back to me in the next 24hours.