Being billed twice for one handset device

Good day, I have been phoning Vodacom Call Centre for two months and no one can assist me and I'm just being transferred from one CC agent to another without any answers leaving me angrier and angrier every time.

I've upgraded about 2 months ago to the Samsung S8. My contract amount is suppose to be R800, but on my monthly bill it shows 2xR500 for my phone. I only have the one phone which I've upgraded to, the Samsung J5 was included with the contract free of charge. I have received the two phones with the two sim cards, I went to Vodacom Century City and they did a sim swop for me so that I can use the Samsung S8 with my current cell nr. No one can tell me why I am paying over R1000 a month for my R800 contract which I have signed up for? Is there anyone out there who can look into this for me and do some proper investigation on this. I feel like cancelling everything!!!!!! I've been a loyal Vodacom customer for over 15 years!!!! Regards Seugnet