Can't understand loan period

Having had a zero balance on my home loan for about a year now and an available balance of R35000 I decided to use R10000 to add to a well-performing investment I have. The remaining term on my home loan is until December 2020, so I assumed the R10000 loan would be over that period. Not so. It's over 3 months! Having been passed through 4 call centre agents, with only the last one being able to confirm that it's over 3 months and that's that, without being able to explain WHY. So now I have a loan that states the remaining period is 11 months and the monthly repayment is R3362!! I was also told I could apply for an extension period for the R10000, but the remaining R25000 credit would fall away. Could someone explain why the R10000 loan is over 3 months and not 11months?? My credit record is impecible. FNB is able to check on this.