Interest not being paid

I have an investment with African and I recently changed my banking details. I gave the bank my new details and it was updated and verified eventually, Till date I have not been paid my interest for 20/12/2018. My interest period somehow got changed to expiry. I had phoned on 31/12/2018 and was told within 72 hours the request will be done. I phoned again on Thursday and was told to give it some more time due to the festive period. Nothing has been done as yet. No feedback. I have to continuously set call backs so the bank will phone back. I am really disappointed at the level of service received. I just want to 32 day notice to be changed from expiry to monthly like it was and for interest to be paid to my new banking details which were sent and verified