I have installed Avast Anti-Theft on my phone. When I changed my sim card on the phone (as my old sim gave problem and I have forgotten I have Avast software installed in it),it continues to send SMS alerts to my family members that I have lost the phone each time I switch my phone on. It has been happening for several days already and trust I will need to bear the extra cost of SMS.

How can I stop this? I am not a phone or internet savvy person. Possible if you can help to give a step-by-step instruction on how to stop this from happening? Thanking you in advance.