I had the exact same issue and it was because we had Netflix active on our T-mobile One Plan before and just removed it on t-mobile.com. I was able to fix it solely using the web portal after you log in t-mobile.com.After you log into your account, click "Contact Us" on the top navigation. And under "Plans & Usage", click "Add family allowances". As the account own, you need to check "Family Allowances". As what other said, this could be a bug from t-mobile that when you remove the Netflix service from your account you also remove this "Family Allowances" feature as well. Apparently without this, you can't make calls.
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