How do you stop the SMS messages?

I installed Antitheft. From then on the two phones I had on my list started receiving sms messages that the sim had changed - it hadn’t. In the end , I uninstalled Avast as it was giving me too much pain and aggravation. The sms messages are still continuing. How do I stop them please?

Many thanks for any help

Neil

Can you please drop me the SMS text (anonymized if you want)?

Reinhard

Apologies for the delay. I have sent you a private mail with the text message.

Neil