Bad bad bad service !!!!

I upgraded in January, got a massive bill, phoned Vodacom and they said it was for pro rata and the outstanding balamce of my old phone that is divided into 6 month. New debit order for the month of February went off, almost 3** more than the previous bill ????? HOW does that work ? The vodacom app is USELESS, it doesn’t work just says oops error occurred when I want to view and check the bills. This is outrageous how am I biled more money this month than the other month ?