Double charge on Subscription service

Telkom is charging me double my subscription services and I'm always logged on to work wifi during the day I don't use internet with my cell, I only Ligon to Facebook and instergram at night, I want Telkom to explain to me why are they charging me double my subscription for October and November 2018 but Sep and the past months I've been charged the correct amount and I've been using my cell the same way ever since I got this phone. I want someone from management to contact me coz your consults don't have manners, the chat in the officer while the customer is on line.