Random SMS texts to private number

[Pixel Rogue]

Every 1-2 months I get a new blind SMS text to my private number from 'an investor' wanting to purchase one my multi-units. Property is not for sale. Each time I ask for detail on how the number was acquired as it is not a number listed on any public records, and each person (or 12 now) refuses to share - deeply guarded secret . Personally think a realtor from the past added my info to a service (ie. Lead Sherpa.)
Love it when they give the predictable 'Cash-as-is pitches."

Anyone else run into this? What are the most popular SMS services being used and I can try reaching out that way to stop the spam to my private number.