Billed without informing me

In Jan 2015 I received an sms from Autopage informing that I can upgrade my tablet contract.<br> I went to the Montana store and did my upgrade, the monthly contract went from R349.00 to R329.00 per months.<br> Upon receiving my April bill due end April, I have been billed for both of my devises. er the consultation it is for the inconvenience of the upgrade, and the migration of the pachake.<br> Not once were I informed if I did my upgrade 4 months in advance I will somerwhere down the line pay for 2 devises! Autopage contacted me informing me I can upgrade!<br> I would like te have the amount billed for the old devise credited!