Not helpful assistance vodaworld

We went to vodacom in Midrand on Saturday,we went to buy a product on a contract ,but was given a voucher,to fill in online at home ,then when it's approved ,they will deliver the product ,but we are charged on the contract automatically,if they approve the online voucher or not ,then we have to drive all the way back to vodaworld to sort it out ,the fact that,Vodacom branches can't assist customers ,why don't they just assist at vodaworld,now it's Up and down driving , and they can't assist via phone !