Payment not allocated

I took a loan with izwe in 2017 and settled the amount in 2019 October.i paid R11000 Fnb account for izwe as I have used them before.now I get calls from rcs saying my izwe account is in arrears and they cannot allocate it from the fnb izwe account and I was supposed to pay it to standard bank RCS account.how do I pay RCS if I took a loan with IZWE.If IZWE and RCS are working together why are they not communicating to allocate my payment.