Impossible to stop SMS being sent after change of SIM

I have noticed that I am being charged for international texts, which after searching transpire to be to do with Avast anti theft. I have recently change to a different provider and obviously you get a new SIM, however I cannot see which of my phones the SMS’s are relating to as the phone I use did not have AVAST anything on it. I have installed both Avast Mobile Security and Avast Anti Theft in order to at least see if there is a way of disabling it, but no I now seem to be updating this device with Avast. I DON’T WANT AVAST. I WANT TO STOP THE TEXTS WHICH I AM BEING CHARGED FOR. Please just a simple method of stopping these texts. I realise that AVAST don’t make any money from the texts, but my provider does and I am paying. This is not acceptable. I can’t even look on my avast account to see what phone they think I need to be told about as I am not actually getting any emails.
PLEASE JUST LET ME DEACTIVATE MY WHOLE ASSOCIATION WITH YOU I WANT NOTHING TO DO WITH AVAST AND DON’T WANT TO BE CHARGED FOR THESE TEXTS…

HELP!!!

https://www.avast.com/faq.php?article=AVKB135
https://blog.avast.com/2014/07/02/how-to-prevent-unnecessary-costs-of-avast-sms-notifications-when-replacing-your-sim-card/