2 phones ready for upgrade paid off and not showing one of them

I have an iphone 12+ and a 10 with service through xfinity.  I chatted with customer service for hours trying to get it straightened out.  It will not allow me to upgrade the one phone of the two I want new.  I have read this is a know issue and everyone I have read has lead to nothing but frustration and it not being resolved.  I want to upgrade my phone- I have a $200 credit through the rewards program that expires soon.  Please contact me to get this issue resolved. Thanks.