AFRICAN BANK REAP OFF

I would like to express my dissatisfaction with the service and conduct of the officials of African Bank Head Office , regarding payments due to me for serviced I'd rendered to them. I've been rendering maintenance services for them since 2017 and sometime late 2017 , I got an instruction via email from Mandisa Makhaya the lady who had always given me instructions on their behalf ; This to attend to faulty aircons at about seven of their offices. I dully did and in some of the offices Purchase Orders (PO) were delayed due to their internal processes but I was instructed to proceed anyway. To cut a long matter short , African Bank is refusing to pay me for work I did in 2017 late to 2018 early up until this point ( 10/01/2019 ) and their excuse is that POs were not issued. I should point out that I was instructed by their official to proceed without a PO as has happened in other instances and they paid before. I would like to be assisted to get them to pay me for my services and cost for parts I bought , since this is negatively affecting my business. I've exhausted all internal avenues with their head office in Midrand and have had no joy. I was attended to by a very helpful Adiel Pursad who is at their forensic investigations and a very useless operations manager called Nivash Manulal , who has from day one indicated no willingness to help but was fixated on the idea of not paying us , over and above his unilateral decision to terminate our contract without proper communication as to the reasons why. If he had his people in mind , as he was new in the position when this happened , he should have at least paid us and came with a lame excuse of terminating our contract. I would love HelloPeter to help me resolve this and also refer me to other relevant institutions who can assist my company in resolving this matter amicably.