False promises made

I received an sms offering me a free upgrade to Premium on my second month on Compact Plus if I upgraded to Compact Plus by 31 March. I then took up the offer and took the offer. I have since paid my 2nd compact plus subscription but I have not been upgraded. I called the call centre and spoke to Nontokozo who told me that the offer is only applicable to a full month but it says nothing of the sort on the sms that I received. When I tried to explain that to her she said that it says full month on her system. So if you send texts to me as your customer, am I supposed to smell the missing information?