Account on Hold 7th Feb 2024 for no reason

Good day ma/sir My names are Okozi Gift Oke and I bank with first national bank(fnb) for some years now with Account number *** and it's my personal account,i'm a waiter and I work in a club called Booth Night Club and ROOM 130 Bar in benmore sandton some time last year September 2023 a client of mine by name Frank who came to our venue to chill on 9/9/2023 and bought some drinks of R8060 included with my tips R8,866 and did not pay same night though I know him very well and he usually makes payment the next day.so i paid with my own money by transfering from my savings pocket from my fnb account and the following day i sent him the bill so he can pay me later that day i received a payment of R8,500 into my account and he forwarded the proof of payment to me.later i noticed my account was blocked by fnb and when I noticed that I quickly reached out to the bank to find out why n the reason with the help from the bank we were able to reached out to the investigating office who is in charge of the case and I spoke to her on the phone and she told me she will send an email to me please I should respond to the email,on 29-9-2023 I received an email from the investigating office in charge of the case by name Abrahams Jade Fnb was notified on 2023/09/19 that the below payment was received into your account number ***.the matter was reported to fnb on the basis that your account received the proceed of alleged ***** R8,500 Your are hereby requested to provide fnb with the reason for the receipt of these funds as well as acceptable proof of same.this was the email I received n same day I responded to the email by writing and providing the bank with the invoice slip of the bill and I attached it to my email.the investigating officer received my email and later my account was open for me to use from September to January 2024 my account was working perfectly then Febraury 7th 2024 my account was blocked again n I was wondering what could be the issue again I try to call the bank to findout what exactly is the issue there was no good reasons then I went into the bank again and they called ***** department to check and from what they told me they can't see any case except the case of last year September that is on the system which has been resolved already by the investigating officer who I responded to her email she sent me now someone else went back and put a hold on my account again and up till now not even a call or an email from him or her to state the reason why my account is blocked again. Honestly this is not fair at all the treatment I'm getting from the bank I really don't know why he or she is doing this because that matter has been resolved last year already.please kindly assist with my case thanks