Problem with Anti Theft - SMS

First of all I’ve never studied english, so be patient, I will try to do my best but I will surely make a lot of mistake
I’ve tried to install Anti-Theft
I do not have any other number to indicate, but if I’ve understand it right I may use the web and receive messages there …but
the program tell me that I have some app that make send sms impossible but do not tell me what app is
At the moment I use none (not even WhatsApp) so I do not understand what to do
Can someone explain me how to configure the anti theft in the simplest way
Have the chance to block my phone and/or make it sound like “this phone have been stoled” will be ok for me … but having the chance to do it on web

I hope what I’ve wrote is understandable and wait for an answer

Thank you all

OPS … errata corrige … I’ve find out that my phone has AVG pre installed and that I cannot unistall it … what can I do? any trick?