INCORRECT BILLING FOR 20GIG DATA - ONLY 18 GIG ALLOCATED

REF NO 1-38G42ZK I did an upgrade on my cellphone on a in store promotion of R599.00 which included Flightcentre Voucher of R5000.00 and 20 Gig data once-off.

After complaining to the store and head office, I finally get 18 GIG of data - 2 Gig short.

This morning I check my app for billing and shocked to see an amount of R1788.11 I log in to my account and see that I'm being billed for the 20 Gig Data that is part of the upgrade package with an amount of R999.00. The normal cost for the contract is also not R599.01 - why I'm being charged for the free data, I was also not informed when this data that I waited 3 months for after numerous queries be logged will expire which I only received on the 04 Jan 2018. If you only allocated the 18Gig on the 4th Jan 18 how can I have used 2Gig data in 1 day if my phone is on wireless at home and work. Can you please reverse the charges for the data and give me my 2Gig that you still owe me and also give me the expiry date for this data seeing that I had to wait three months for it.