avis car rental

I need help pls

My husband rented a car from avis airport port Elizabeth for 6 months...January was our last month We were supposed to receive a R2600 back from them 30 days after the car was returned ..which means that end of February

As a result of not receiving this money...My husband's capitec account has been in a minus of R7000 that's the amount of rental in total...we've made numerous visits to them and they just ignoring the issue...weve been to capitec and they sed that they can't clear the R7000 from his account because they haven't received an authority from avis to do so We are so despondent because we can't use the capitec account and my husband has received a call today from Avis that He owes them a R700 and he was now handed over...what the hell...I don't understand Could you please offer a hand of help