Lack of duty to inform by MTN Heidelberg Mall

I don't even want to give them a star. I went to look at phones as I was due to upgrade soon. The ladies informed me that I could upgrade that day. After the upgrade we received a bill stating that we owe an R1600 penalty for an early upgrade. We asked multiple times during the day of upgrade if there were any extra costs to which the response was no. We are being forced to pay this money after we were repeatedly told there were no extra costs. When we spoke to the branch their only response was that we should have been told. I feel it is extremely unfair to expect an out of budget payment because of lack of information. MTN is just putting their hands up and saying we must pay. The branch is in Heidelberg Mall and I believe the lady who helped us(or rather cost us) is Thabiseng.