Device credits removed without being warned.

Early August 2024, I visited a local Xfinity Mobile store to purchase 3 phones and 3 lines. We received a promotion for each device, $500 device credit split over 24 months, per device. 
3 Months later in November 2024, my wife's Galaxy ZFlip 6 stopped working. We decided to visit the local store again to see how we could rectify the situation being as the device was brand new, and not damaged whatsoever. Unfortunately we did not purchase the device insurance. The representative in the store advised we should purchase a temporary phone and line, while we waited for Samsung to repair her device. At that time the ZFlip 6 was just released, so the parts were in VERY limited supply. We obliged to getting a new cheaper device to hold her over until hers was repaired. We purchased the device and line, the employee stated we could switch her current number to the temporary device, so she could continue receiving calls and texts with her number she has had for over a decade. 
WE were FINALLY able to have the phone repaired in May 2025. We then were able to get her phone switched back over to the ZFlip. 
In August of 2025 I noticed our bill had not gone down back to the original balance from PRIOR to this whole fiasco, after cancelling the now un-needed line. I knew it would be $10 more than the original balance because I was still paying for the temporary device, but no line. 
That's when I check my bill and find out, the ($500 split over 24 months) credit had not been applied to the Zflip6 SINCE NOVEMBER 2024. I have read over the contract for device credits numerous times at this point, and no where does it state that changing the phone number would automatically cancel your device credits. 
I was NOT informed of this by the representative, who ADVISED US that we should just get a temporary phone, line AND switch her number so it was a seamless transition. 

All of this to say. Why did the representative advise me of this, knowing it was incorrect? Why was I not made aware that this would automatically cancel the device credit? The phone was never once disconnected. It has been active as well as being paid for, on time, the entire time it was unusable. Why is it not stated in the legal agreement? My promotion had nothing to do with a trade in, nor a port in from another company. I was simply doing what I was obviously so wrongfully advised by an uneducated employee. 

So be aware. Do not listen to the employees, they do not know what they are talking about.