FNB to FNB NOT IMMEDIATE!!!!

Yesterday a customer paid me from FNB to FNB for the purchase of my vehicle , they did the payment in front of me in 6 different amounts , 1 of the payments went through but the others did not, we called FNB and they said it will take a few hours to reflect and that the payments did in fact go through but now on the next day there’s no money in my account and when I call FNB they say that they cannot check for me and that the buyer must call and check , how am i supposed to trust what he says? Why can FNB not check for me when the money was supposed to go into my account.