Hi,
if you
a) don't know your PIN
b) didn't set up your PIN recovery number
c) didn't connect your device to avast! Account
then there is not much I can do to help.
If you can access the device in a normal way and just can't get into Mobile Security/Anti-Theft, you can try to uninstall both of the tools via your PC. Search the forum for that, there should be some kind of a walkthrough somewhere.
Filip