FNB complaints not responding

I laid a complaint on hellopeter about FNB on the 15th, I got a call within 30min from the bank to acknowledge that they have received it and is looking into it, and that I can expect a call before the end of business of the same day. today is the 18th I've not heard from them. I have phone the original person that was going to deal with my complaint twice, he does not answer is phone or return message, Impossible to get answers, last person that was dealing with my claim, says she can't help as the file is now with complaints, and the complaints department is ignoring me, what to do?