Blacklisted to only one carrier

[Android Central Question]

My Galaxy S9 Plus (model number ending in U1... Bought from Samsung?) recently stopped receiving texts phone calls and LTE data from my service provider T-Mobile. Upon further investigation it appears that the IMEI is blacklisted online. It was not the case when I bought it. I purchased it from a third party who I no longer have contact with. It had a clean IMEI at the time. T-Mobile believes that it was maliciously reported to be stolen and thus blacklisted. It is not a T-Mobile device. I recently switched from MetroPCS a month ago so that may have something to do with it.. The interesting part is I can still get service by putting in a Verizon sim card and an AT&T SIM card. a Verizon rep said that they do not show the IMEI has blacklisted and could put it under their service. Is this a mistake on T-Mobile reporting it as blacklisted or is it just taking time for the blacklist to show up on other networks?