249-799-5500

No idea who this is but I keep getting spam texts from.this number. It says that I am part of a group text although there are no words.

Forward unwanted spam/scam texts to 7726 (SPAM) and let your phone service provider deal with them.
That number was set up by the phone companies to combat spam/scam texts and they can shutdown offending phone numbers.
Never reply with "STOP", scammers will not honor the request (they have no honor to begin with) and it only verifies that they have texted to a valid number with a person who reads their texts.  It will not STOP the texts and may actually make them more frequent.
Never click on a link in such a text as it may cause malware to be inserted on your phone, and even if it does not, just as with replying "STOP" the scammers will know they reached a valid number.
Do not repost any links included in the text message to public sites such as this one.  It may subject others to malware if they click on it or, in some cases, it may reveal personal information posted on the target site of the link.

Also, report them at:
ReportFraudFTC.gov