Cell carriers are maintaining a sharing spam caller lists. Your number may somehow get placed on these lists inadvertently or intentionally by a called party suspecting the call is a spam call.
Telephone numbers are listed and delisted by completing the form here: https://callreporting.t-mobile.com/. To delist your number, select the "Not a Scam Likely Call" radio button and enter your phone number where required.
To further delist your number should the carrier sharing appear to not be working, use these links as well:
www.reportarobocall.com (sprint, verizon, US Cellular)
Please allow up to 48 hours for the databases to update.