Changing the package R492.00 to R927.00 without the knowledge of the customer

My name is Bonisile Nkosingphile Gabisile Zulu,. Account ***0. My package was changed in 2017 from premium to the next package and since then i've been paying my account not exceeding R500 include the explorer R95 option. I've also changed the date from the 17th to the 27th of each month. January 2020 i was informed that i owe R927.00 which came as a surprise because i normally par R492.00. I did call but the guy that i was talking gave no assistance to me. I requested him to check my statement for 2019 and see the package that i'm on and to check where did the change happen and by who. He refused.