Poor service and incorrect payment information

I settled my revolving loan with FNB on the 15th of April. On the 4th of May I received a paid up and closure letter from FNB. This morning (12 June), I contacted Experian to check my credit report and they indicated that the revolving loan is still reflecting as open and that a my last payment has been late. This is negatively impacting my score. When I contacted FNB they told me that they cannot assist me and that I have to go into the branch to speak to the credit manager regarding this. When I phoned again, I was rerouted to about 5 different departments, of which neither could assist me, and I waited on hold for almost an hour. This is unacceptable.