unlock cellular part of ipad pro 12.9 1st gen

yo. i bought an ipad pro 12.9 1st gen from a dealer on ebay... the cellular part of the ipad pro 12.9 1st gen doesn't work... it's probably locked by the previous cell carrier and i get that the main way is for the previous carrier to UNLOCK the device...

wanted to know if anyone knows a work around?

i've googled everything and it says to pay for this and it will unlock it but i know it's a scam...

i already contacted the dealer and tried to get info from them... they basically said they don't know and allowed me to return it... i'd like to keep it if the cellular portion can be fixed...

thx