This is not unusual. Someone told me they had a device that would open all garage doors. Kids would go up and down streets opening every garage door. I lock my door from the inside and when I am not going to use opener.

call the # on the door opener and they will email you the instructions (MVP opener)

changing garage door signal
 

We had an awful neighbor who had a box that would change your code so that we'd come home to see our garage door open. It got so bad we had to call the police.
My recommendation-unless you are very good with tools, find someone to change it for you. A lot of people change their codes and then whenever they close their doors, a neighbors opens!