Assigning a contract under false pretenses

The other day a Vodacom sales person showed up at my aunt's house while I was visiting. He told us that they were busy installing fiber in our area and asked if he could have a moment of our time to tell us more about it. Having wanted fiber for a long time now my aunt and I went outside to talk to the guy. He did not give much information, but said we can fill out a form and more information would be sent to us. I agreed and started filling out the form. I started getting suspicious when he asked for my id nr, and then I realized that he wanted me to sign up for a contract. I explicitly declined and told him I'll go read up on the internet at home before I decide. He then pulled out another form and said that I he can save me time by emailing me the information. I just needed to sign that form to give permission that they can "spam" me. I wrote down my name and email and signed that one page. I did not want to hand back the first form (with contract options) that I had filled out about one third. He asked to have it back and gave some or other explanation about how he would have to account for it. Reluctantly I handed it back. Two days later I was contacted by Vodacom requesting 3 months payslips so that my contract can be finalized! I immediately requested a copy of their documentation. On it I saw that the remainder of the form from that day had been completed by someone else. The final page he requested me to sign so that they may send me the t's & c's ("spam") was in fact the final page of the contract! We are shocked at how this person was able to deceive us like this. He had filled out an entire contract under my name! This after having been told more than once that I did not want to take out a contract without discussing it with my husband and reading the terms and conditions. Surely this could not have been legal? Vodacom may rest assured that neither me nor my Aunt will ever take out contracts or conduct any business with them EVER! I'm pretty sure this will apply to the rest of my family who have also had very bad experiences with them.