NEED a Refund by MTN

Mornings MTN I need a refund for my phone contract with MTN I paid MTN without knowing that my account is handed over to NIMBLE GROUP so and I paid NIMBLE GROUP at the same time I settled my contract. Now I battling to get the refund I have proof of payments with me now ... it's been five years now no response on the matter I even went to NCC I got their email saying they will try to help still no response.

Thank you