I got a fake call from t-mobile, where do I report that? No, I'm not sitting on the phone on hold to do so.

I got a phone call from a number that does not check out as t-mobile's, they're claiming to be from sprint/t-mobile. I don't care to dig through todo the forum rules to know if I can post the number here, so I won't.

Is there an email, chat service, or any other web-based means to report these events? Please don't tell me to download the app, I'm not interested in bloat.