Promotional offers to valued customers .....lies

On the 2nd of October 2015 I received a text message from Mtn stating that if I deplete my 1 gig of data I would recieve 2 additional gigs of data for free , again on the 9th the same sms was received , on the 18th of October my 2 gigs of data which I purchased, had been finished there after mtn had given me 1001mb free , on the 19th of October the free data was reduced to 200 mb which was odd upon checking my data usage the meter shows that from the 18th till the 19th only 140 mb was used but yet a total of 861 mb was unaccounted for , firstly mtn mislead me to finish up my data secondly they given me half of what was promised and thirdly the data dissapeared on its own I have been with mtn for a long time now and if this is how they treat their prepaid customers I'm glad I didn't opt for a contract , I contacted the customer care to which they cannot find the promotional sms or any data been given to me yet I have proof of the sms and data been loaded , how dissatisfied and upsetting it is for MTN to be lying ..