Deduction Date Changes without Authorisation

I have a Home Loan with Nedbank Home Loans. I signed for deductions to go off my account on the 25th of every month. On a monthly basis I get an sms that my deductions will go off on the 22nd, which i reject but they still deduct on the 22nd. Why even bother giving me an option to reject the new date and why would you change to a date i didn't sign for. I have called and done all i could to even being kept on the phone for over 11 minutes, with no progress. Please keep my deduction date to the 25th of every month which is what i signed for.