promotional master debit card thru Citibank expired -how to activate as not used

I found my debit card which was given when i updated my daughter’s phone on my plan, i was given a debit  master card but had misplaced it. i had moved so was going thru all the papers & found the card still attached to letter in an envelope it came in. I hadn’t used it at all & the card has expired.

when I try the number on the back or website it says card not recognized.

called T-Mobile & they told me I had to call the bank that it belongs to but citi has no idea & they told me to call T-Mobile. Getting a lot of runaround. can someone please help as it’s couple of hundred dollars. 

I want to give that to my daughter now as she’s older & it would come in handy for her at college.

Thank you so much