Samsung tocco thief reset my security code

Hello,

i got the samsung tocco lite and i activated the phone tracker using the code 0000, not really knowing what the phone tracker was or about i activated it anyway. about a month later my phone was stolen, but i got it back thanks to the phone tracker. delighted, but the thief reset my security code, im not sure how but they managed to, so now i cant get into my messages, any suggestions?