Pro Rata *******!!!

I recently opened up a new contract with you guys at the telkom shop in Mall of Africa. That was on the 18th of July. I was advised that I would be billed end of August and that July I would be charged a pro rata amount. I have received my invoice and am shocked that I now have to pay for the full amount for the device when I had it for less than half a month. THIS IS RIDICULOUS! WHY was I not properly advised. If I had known I would have taken the device 1 August. Furthermore I called the client care services and was told a manager would get back to me..its been 3 days and no one has contacted me. I'm thinking of just bringing the phone back and cutting ties with you guys this is such poor service and you do not value your customers.