£50 new start up bonus help

Hi , I had a virgin media Salesman come to the door few weeks ago and wanted me too purchase virgin as he noticed id been looking on the website. Long story short , I purchased a package to start in march after my other provider ends, which is about £80pm internet and TV and he promised I would get a £50 new bonus discount and even messaged me to say that he has spoken to his regional manager and the £50 discount all went through and it would come off my first bill so instead of £166 ISH it would be £116 ISH. Spoke to virgin yesterday and they have nothing on there system about the discount and the salesman isn't answering texts etc now.  How do I speak to his regional manager or what can I do sorry from cancel it as not live till march.