Vodacom contract missing

My husband had opened a cell phone and data contract for our son, at the Vodacom Chatz Fleurdal branch, sales lady Helena Oliphant. We have no problem with the cell phone contract, but the data contract was incorrect, we had asked for the Top-up option on our application form, but instead it was made an open account. The account is now outstanding with a big amount. We are looking for the enrolment form, to see who was at fault. Many emails and visits at different branches and Vodacom is still not answering our question, where is the contract, that we signed.