SAFAIR ARE YOU IN THERE

I cancelled a flight for my sister. I got 50% of the total back in the form of a voucher. I am going to visit her instead in December, so tried to use the voucher to change the flight and put in my details. Could not do it. First called, the machine was doing all the talking. Could not speak to a person. Then I tried to Whatsapp, and true to a robot, if you don't ask the correct question, you will not get the right answer. All I want is to be able to use this voucher, and speak to a real person in order to do so. Is that too much to ask??