Get your staff to actually call back when they promise to call back.
Please get more staff and training them to follow through with commitments. If you promise to call back do it because you will loose customers and it costs less to keep the ones you have than it does to win new ones.
I apologise if you've not received a promised call-back and I'd love to resolve this for you. If you require further assistance then you can reach out to us via social media, live chat or secure mail and request for a call and we'll definitely be in touch. ^TK