FNB

I sent money from my US account to my FNB account 2 weeks ago. The money reflected in my account and once I saw it was there I proceeded to buy some furniture on Facebook marketplace. The transaction for the furniture went through without a problem. 2 days later I checked my account and it was overdrawn by R3560. The R4585 I had sent myself was no longer reflecting in my account and there was no trace of it ever having been there. I have spent the past 2 weeks texting, emailing, sending proof of the transaction , I had taken a screenshot of my account showing the money was there as well sending them the proof of the email they had sent me stating the money had been successfully deposited into my account. Now all I’m getting back from all the emails I’ve had from them is that there is no record of the transaction and that I should get hold of the bank I transferred the money through. No resolution. Very disappointing FNB. I have lost faith and would like my money back please. What other proof do they need??????