Monthly Installment on my account

Good afternoon, This month when I received my monthly statement my instalment was almost R500 more than last month (haven't bought anything in the last two months). When I phoned Customer Services I was advised that it is an mistake on their side and it will be rectified before my Debit Order Date. However today, 2 days before my Debit Order day I received an call from their Head Office advising me that the monthly percentage was increased and that this new instalment will be my instalment from now on to enable me to pay of my account more quickly!!! Did anybody else had the same experience this month??