Security concerns

I recently, was my own fault not protecting my visa card but got scammed, I chopped the card but yet somehow someone accessed my amazon account and tried purchasing something just the other day. I only use this laptop for amazon. My concern is how to stop people from getting access to this browser through shared wifi and the person got into this laptop through the smart tv in the part of shared accomodation. I matched the serial number of the device to the device that appeared in devices in my control panel which I never authorized to access my laptop. I dont allow any access to my "network" to anyone but somehow someone got access. Any advice would be greatly appreciated. And everytime I tether with my cell phone its alwys a new network that I get asked by microsoft if I want to allow discoverable which I dont, but I usually have 80 -100 networks due to every log in with teher and wifi booster. Thank you