Calls getting cut off

Phoned FNB home loans call centre in May with an account complaint and discovered today it has not been solved satisfactorily. Same thing I experienced then happened today - getting cut off - phoned again and again - have to listen to all the same recorded stuff again until my phone's battery dies. Not to mention the cost of the calls. Now I have to spend my afternoon on the phone again tomorrow. How can I get them to phone me to rectify their mistake?