URGENT trade-in discrepancy -$700 promotion vs $185 assurant accepted offer

I need help with an Xfinity Mobile trade-in that expires on September 21, 2026. On August 31, an Xfinity representative confirmed a $700 promotional trade-in credit for my iPhone 13 Pro Max, including $19.44 per month for 36 months. I have now received return paperwork showing an “Accepted Offer Value” of only $185. I do not want to surrender the phone until Xfinity confirms that the full promotional credit remains intact. I need this escalated urgently because of the trade-in deadline.