Two questions to start with
Was the message advertising a product or service? And did you agree to receive it? Save the full thread, including the first message and any opt-out reply.
Which protection fits?
Marketing texts can fall under Do Not Call protections. A separate claim may involve use of a qualifying autodialer. An automated-looking text, short code, or mass campaign does not by itself prove the legal ATDS requirements.
A text-only message is not a prerecorded-voice call merely because a machine sent it. The specific rule, your consent history, and any exceptions need review.
When you already replied STOP
Preserve the reply, confirmation, and later messages. An opt-out can matter even if you originally signed up. Tell us whether later texts came from the same sender and what they said.
Example to discuss with us
A company sends repeated promotional offers to your personal number even though you do not remember subscribing, or continues after you unsubscribe. Include any earlier purchase, online inquiry, or signup so we can assess the complete history.
Keep exploring
General information, not legal advice. Laws and interpretations can change. An attorney must evaluate your specific facts and any deadlines.