FNB messed up my credit score for no reason and Home Loan since declined!!!

My credit score was fine in the green area in the app and everything was going smoothly and wanted to apply for a smart device through FNB which I did qualify for with my credit status all of a sudden in less than a space of a week when I app**** for the device I was getting declined?? I had no missed payment or anything only a 1 month in arrears with mr price but that was in April and I have caught up with them like the end of that same month and when I checked in June I was in the green with a good score but for some reason in july all of sudden my credit goes horrible and I have a low low score because of this which I dont understand because this 1 account was caught up with and never missed a payment again with them so what happened? I was since declined a home loan that my wife and I so desperately needed and it would have been our first property and now I dont know what to do because of this and FNB has not called me themselves to speak to me and understand my position and how this is a problem that I am so worried about... I am disgusted and so depressed because of this and just feel as if nothing is being done about it