MWEB overcharging my premium

My account was activated on the 7 th of April 2025, i was initially billed 249, then later this month i was billed R 786 .64 instead of R 399.99. When i registered i was told i will be billed R399.99 for the next 6 month since they are running a special. i have tried enquiry on their mobile mweb app and on their facebook page however there is no response.