If someone has gotten a hold of your phone number and is using it maliciously, you can do the following:
Contact your service provider immediately to inform them of the situation
Ask for a temporary freeze to added to your line so scammers can't use your phone number
Contact people you know to warn them about the situation as they may become targets for the same scam
Document all of your steps
If your phone was lost or stolen, it is important that you report it
Change your logins for your bank account, email, and social media