Discount Expiry

I have called African Bank collections section on 06 April 2016 to find out about the 20% discount offer on my two accounts (it was offered in March). I was advised that the offer is still valid until end of May 2016, I then ask family and friends for assistance which I got. I settled the first account (***) on the 15 April 2016 with the 20% discount without any problems.<br> <br> Today I called them to make arrangements that I will settle the second account on 22nd April 2016, and now I've been told that the discount is at 15% which I did not budget for and I do not have any other means to collect the extra 5% to be added. <br> <br> They claim that all their calls are recorded for quality purposes, I'm just asking them to check those calls and tell me why the expiry date has changed. also note that I have an email on my position that also equivalent to my claim.<br> <br> Kind regards,