MTN refusing to change my account to Pay As You Go

I went into the MTN store to cancel my account, they gave me a form to convert my account to Pay As You Go which in essence is the same thing. They told me to fill it in and email it to the email address on the form. I did this, got an automated response that my email has been received. Some days later I got a reply from them saying that I must phone a specific number. I rep**** asking why this is the case when the form has explicit instructions on what to do. That was a month and a half ago. All the while they still charging me.