Microsoft software installed with possible scam

Hi, I bought a very cheap Microsoft 365 on ebay, and few days after we got an scam email: I got an email from a client advising a "new" bank account, some how the scammers replay from a email I sent from my accounting system XERO. I have runned Bullguard and I keep receiving intrusion alert pretty much every day. Malwarebytes detected some threats that were put to guarantee, should I factory reset the laptop or how do I make sure it is clean, please help!!!