MTN LTE Daylight *******

I registered for a month to month LTE contract with MTN on the 29 January 2024, made an upfront payment on the same day for R437.61. I returned the router to the store and requested a cancellation on the 09 March 2024, upon which I received a reference number and was told to call the call centre to cancel with the reference number for the return of the router. I called on the 11 March 2024, and was told that the contract can only be cancelled on the 11 April. I am now still receiving claims for payment to the amount of R849.70, when my upfront payment should have covered my month usage, from 01 February to 11 March 2024, with only a small amount due, and not the amount of R 849.70. I have called the call centre several times, with no-one being able to resolve my query and MTN is now sending threatening sms’s to affect my credit score. R1278 for 45 days of LTE usuage, daylight *******!!!