Wesbank bullying tactics

I financed a vehicle through Wesbank, paid every month for 18 months then took early retirement. I adked for a settlement amount om their website and got a letter giving me the amount and date untill it is valid. I paid the settlement amount in full before the expiry date but now they claim that there is intrest outstanding from the date of my last payment plus a R6 000 early settlement fee because I did not give them 90 days notice that I of the settlement!! My argument is that they should have included all this in yhe settlement amount THEY provided See you in court Wesbank!!