National health laboratory services

My husband had a bill By NHLS, which was handed over to MBD which we paid up in full in 2018 which we have a paid up letter. A few weeks back we got a sms from Creditintel with the same ref that was handed over to MBD , that we still owe them! When I called Creditintel the said cant assist cos it’s my husband details and can’t give information to me! I than call NHLS spoke to a CHarles which he said I need to email the statements and paid up letter from MBD to him which I did, and till today still did not get feedback from him! I don’t know how they operate and make money out of us if we have proof that is paid up !