* This could be a Federal Trade Commission problem. T-Mobile, like all major ISPs, has made public representations about upholding net neutrality principles [1]. These voluntary commitments were part of the Trump-era FCC's rationale for repealing net neutrality rules. Breaching the commitments could constitute a deceptive business practice under Section 5 of the Federal Trade Commission Act.
* This could also be a Federal Communications Commission problem. When repealing the Obama-era net neutrality rules, the Trump-era FCC left in place a set of transparency requirements [2]. Making an inaccurate statement about network management practices can be actionable under that remaining component of the FCC's net neutrality rules.
I haven't seen a comment from T-Mobile, so to be clear, that's just based on the report.
[1] https://www.t-mobile.com/responsibility/consumer-info/polici...
[2] https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A...