Fnb personal loan

Don't take fnb personal loan those people are ******* so I had paid my monthly instalment on the 25th this month and amount was reduced accordingly and then the next morning it had increased back to what it was and I was debited again today I looked and the amount is generating interest at a way over rate then what I had agreed and signed up to calculations at that rate means indebted for ever, I don't know what games they playing behind the scenes even remaining term still remains the same even after paying.