Free Whatsapp..What free Whatsapp??

When we bought the sim card for my daughter the people at Cell C said the WhatsApp is free, it was free for a few months but now we have to keep on loading airtime and airtime, what happened to all free is this exactly the catch? We had phoned a few times , call center said you must just have R5 airtime ok good and well how do you keep the airtime there if you guys keep on taking all the airtime for data?? This is seriously not funny don't promise your customers something and then after a few months start robbing them any way.. I would like to have this thing whatever it is fixed a.s.a.p. and what's better this is my daughter's phone and when we phone to try and get the problem solved the refuse to assist....