Trying to upgrade

I have been trying to upgrade for the last 2 months at the Langeberg Mall MTN shop as instructed by MTN message on my cell phone. A Sony E4 was on offer for R139.00 per month with R100 air time, 200 sms and 300mb of data. After going to the shop 6-7 times from middle May when the phone came on offer and being advertised with above specifics. No response came. Only after I have been to the shop Yesterday 20/7/2015 asking about my upgrade and been told the previous week that it is still the same price, do I get a call from the shop today 21/7/2015. Telling me that if I want the that deal I have to pay more for the same contract and cell phone.