Xfinity

When making my decision to switch to Xfinity, the territory sales manager stated in writing that he could provide me with a $300 “bill credit” as part of the transition package/offer.   The manager has since left on medical leave, however knowing this agreement was made in good faith, I would hope Xfinity will stand behind a commitment from a member of their team. 
Who may I surface this matter with.  I can forward supporting materials to document this position.