Invertex and DMC collecting for same debt - is this legal, please help

2 DIFFERENT DEBT COLLECTORS COLLECTING MONEY FOR THE SAME DEBT

Kindly asisst as i am being harassed by debt collectors invertex and DMC i.e 2 companies for the same direct axis debt, i have already paid invertex over R7000 plus in R500 debit orders. When DMC called me a month - 2 ago negotiating a settlement amount, i throught this is the same company and i have since deposited R3000 as per the attached payment proof. I have now just picked up that i am paying 2 different debt collectors and have let both companies know about this, but neither one of them is considering refunding me as they both claim i should be paying them.

I have told both companies that i will escalate this before making any new payments and since then i am being harassed by invertex calling me throughout the day demanding more money. I am hoping i can be asissted and a refund and wayforwad facilitated. * I have no issue paying what is due, but i cannot pay 2 companies for the same debt - is this even legal?

DMC REF: Direct Axis//Ref:85250154372 CONTACT 043 7024600 INVERTEX REF: INVERTEX VTX882265 190625, CONTACT 0127562444