The inability to properly settle a loan

I have a personal loan with FNB that I have settled on the app. I have used the call me back option on the website to insure closure. However I have received NO response! I used this method as the call centre staff is totally ***********. When calling into the call centre the agent was speaking to her colleague before acknowledging I was on the line. when I told her my query she transferred to the next department without advising me what's going on where I had to wait to be serviced. I dropped the call as I was on hold for more than 5 minutes during transfer. Now FNB wants to charge me interest on a loan I've already settled. Can I please have someone call me back so that I can close this loan!

FNB is supposed to be a user friendly and innovative bank but the incompetence of your staff brings down your brand.

Please call me urgently