Hi @Gabriel L. ,
Welcome to the Community!
I believe that if these customers had previously consented and nothing has changed about the business except for the parent company/owner, then it should be fine to message them correct? Assuming nothing has changed about the mailing list or the business itself of course.
This could be something to take as a precaution and just send an email to collect SMS consent again. This would A. Clean out and refine your active mailing list for SMS and B. You will ensure that people are not getting SMS when they did not consent post-business ownership change.
If you believe you received SMS consent from this subscriber in the past, you could upload them into Klaviyo with an SMS consent timestamp. This will allow you to message them back.
Here's documentation on the process from our Help Center. At a minimum, you'll need a csv with two columns: Phone and Timestamp.
Hope that helped,
Alex