Sounds like you have a virus or bad app. Malwarebytes won't tell you if it is either of those. Try running a good deep virus scan. Then, if that turns up nothing, try uninstalling any recent apps, or recent app updates. Should that not fix it, then you may well have to save your personal stuff off the phone (to a google account, computer, etc.) and do a full on "Hard Reset" of the device to completely clear it of all stuff. Then readd your personal files, contacts, etc., again.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the phone.
Be sure you back up any data you want to keep, to a computer or cloud account...