False advertising

I was informed via their website that a 10Mb line will cost the same as my current 5Mb line. I app**** for the service upgrade and was sent the contract to complete which I did. I waited a week and then phoned to inquire as to the status of the upgrade and was told that it was in process. This phoning and answer were a constant for more than a month and eventually I was informed that the price on their website cannot be given to me but if I paid R300 more than their quoted price it could be done. I would like to know how they can advertise a product for a certain price and then when I have app****, they try and up the price on me. Surely this could be seen as false advertising or are they trying to extract extra monies that is not due to them. I have been a client with them for more than 4 years and surely this is not the way to treat your existing clients.