Phone Plan Selection Issue

Currently have Xfinity mobile with a single line on a by the gig 1gb $20 plan. I want to add a new line and transfer my other phone number from visible and purchase a new iphone with trading in my paid off iphone and get the mobile plus plan because i also will be bringing my paid off cellular ipad and apple watch which i would like the replacement coverage on which is included with the mobile plus plan. My problem is everywhere on the website whether i go to preorder / add new line first etc my only plan options are by the gig or old $45 unlimited plan? The promo says up to $1299.99 off with mobile plus. I also have a member exclusive that says enjoy a $400 bonus when you upgrade to a new iphone on top of your trade in credit when you upgrade on any existing line.

So what i thought i was going to do was add a line of byod mobile plus and then upgrade my paid of 15 pro max for the 18 pro max (or possibly the duo when preorder comes out) and I would receive $1299.99 trade in and bonus $400 in credits too, i was hoping the extra credit would help lower the monthly plan cost because the trade in already covers the full price of the 18 pro max if i went that route. Anyone else experiencing not being able to get mobile select or mobile plus when adding a new line?