Unallocated payments

Kindly please assist, my Cartrack account was handed over to Nimble group and I've made debit order arrangement as of Dec2017 to date for a monthly repayment of R300 which is being debited monthly. But Nimble group is currently threatening me with calls, sms and emails EVERYDAY that the account is overdue and that the only payment received was for Feb2018. I have emailed Bank statement reflecting all debit orders so that they can allocate the payments and have spoken to Rodney (The Manager) till today I have not received any feedback on the account? I have sent several emails and have cc'd Rodney but no response??