BS Upgrade ****

I needed to do an upgrade on my existing number, everything went fine with the lady who helped me until i try to contact your call centre & I am told that I owe R2990.09 on my account. When i agreed to my update I was told I will need to pay the new contract amount & the amount of the old device. I am now told that I need to pay some 'gap account' that the upgrades department created so my upgrade can go through which i was never told about! Why are you people so quick to take our money but cannot give us any solutions? I want to know why I was never told about that amount from the upgrades department. I give Vodacom the benefit of the doubt but you people are forever failing me.