When you take out a loan payable, you should generate a loan amortization schedule. The schedule details how much of each payment goes to principal and how much to interest expense. You use the schedule to prepare your accounting entry for the payment and to check against the bank's loan numbers as a control device. You can generate the schedule by building your own in Excel, or using a pre-made Excel template from the Web, or buying a product like Tvalue.
Sounds like this has not been done properly last year. Anyway, the schedule will get you on the right track. Also once you generate your schedule, compare the current loan balance outstanding that you get with the bank's numbers (call the bank or ask for a statement). If the numbers do not agree, contact the bank and ask for help in understanding why not. If possible, just ask for their actual amort schedule to help you.