Online purchase processed without the discount

I purchased a laptop online which had a discount and when I paid for it the following day it went through at a normal price, I called countless times for help, until a guy by the name of Michael Blignaut tried to assist but also sent me a conclusion which didn't add up when I sent him an email of the calculations stating that their conclusion was thumbsucked and that it didn't add up he never rep**** I've sent him an email to follow up and he still hasn't now I'm expected to pay without my issue being resolved. I hope a manager or somebody can try to help cause now they are telling to go to the store and call head office which is ridiculous and unfair my email address is *** I've got the emails and screenshots. This is just taking advantage of the end consumer cause they are hoping that I'll eventually give up