Fundi is *****ing money from my account

I requested the aid of Fundi to assist in paying up my sister's fees at University of Limpopo. They have been debiting as per agreement. In January this year i requested a paid up letter where they sent me the account details and reference details I should use. I paid the amount that was outstanding which was reflecting on my payslip. I forgot to put in the reference. I notified the admin with whom I was communicating with about the mistake but I sent him the proof of payment. He told me that there is nothing they can do due to failure to input the references. Till this day they are still deducting from my account even after paying the account up. I further tried contacting their head office branch they gave me an email to send the proof of payment, but they claim to have not received them. I even spoke to two other consultants outside of the one I was communicating with initially.