Unfair billing

I have a router which was a contract for 24 months that amounted to R200.00 monthly. The router when I app**** for it was for 20gb which was supposed to be 10GB for daytime and the other for nighttime. To my amazement on their statement it shows that I was on 10GB for day time and night time. My contract ended in February 2020 I didn't renew it but kept on getting the wifi transmission and they were debiting their money on the 20th of each month. In May they debited me R347.56 instead of the R199.99 that I knew of. Now in June got statement which states they are going to debit R447.00 but still getting same bundles. I tried calling them with no luck; if they put me on new contract and increased the premium why not mention it on statement and why the statements amount are not the same. I normally top up the router if it gets depleted before month end. I just need clarity from Telkom how they came about increasing the amounts and not informing the customer. My router number:***