3 months worth of finanace charges debited at once

I check my balance electronically as I do every month to make sure my payment was received and credited and discover that not only is my available balance zero but my next payment due is higher by over R150 than normal, I then open my statement to discover that 3 months worth of finance charges have been debited to my account instead of the normal one month. This has left my card unusable because it is over limit and I will be charged interest upon interest. How is this possible?