Bad service

Good day , I have a problem with MFC NEDBANK . They are financing my car since last year June , I lost my job in November and I asked for 3 months without pay , they agreed and added another 3 months on the contract, the problem is they didn’t tell me that my installment will go high for every month and now I changed my debit order because of the piece job that have , when I checked the installment has increased again and when I ask them they say when you change a debit order you are charged , I’m trying to pay this car but they keep on adding amount that will result me in not affording the car anymore. And they take all the decisions without informing me .