The plain answer is you got robbed.  Now that it has happened you most likely still have something on your system.  The best removal tool and only one with real success in removing most of these is Malware Bytes.  Most anti virus will  not detect or remove anything like you had on your system.  Some will detect and remove the symptoms but not the cause and then sometime later when you reboot there is your problem again.

Download and install Maware bytes and run a full scan and that should remove your problem  I have had to fix several systems with the same type of scam as you had and that has consistantly been the best cleaner.