Do we really have to get new phone numbers if we purchase an iPhone 12?

Trying to upgrade our phones.  We’ve had our numbers with TMobile for 10 and 20 years, 10 years for a work line and 20 years for a personal line. We selected “upgrade” for one phone and when we selected the iPhone 12 it said we would be getting a new phone number AND our TMobile phone number that we’d had for 10+ years as my husband’s work number was not transferrable. We then tried my phone line, which we’ve had since 1999 WITH TMobile (the account has always been TMobile) and it said that number was also not transferrable.  We do NOT want to change phone numbers but we need new phones. Soooo……

I will call a rep tomorrow or stop into the store, but I hope that isn’t what it seems to be.  Would it be because of the Sprint/TMobile merger?  Because that would be sorta dumb.