Hi Jan, it's sad to see
that in 2018 there are still people using windows for online stuff, in the age of hundred gigabytes SSDs where you could have made a small 100GB partition, install Ubuntu or Linux Mint and surf worriless
. If you need to use some MS only program, boot on windows and use it, but don't go online, or you'll get p0wn3d, in the best case you'll mine coins and spread propaganda and spam, in the worst case you'll lose all your money and get you identity stolen.
I have the following advice for you, that may still recover something or at least reduce the damage:
Your Windozian machine was169% pwn3d long ago , carefully remove all the hard disks and shred them away
, or at least boot from a R/O medis with a Linux distribution and wipe them fully.
Then immediately cancel all your credit cards used online and change the passwords to all online banking, social or governmental sites you've used, from a secure, freshly installed, Linux machine, not from your phone (a good chance that is also 169% pwn3d as well).
The go to a computer literate friend and download a Linux distribution, burn a CD or a live USB stick and boot from it.
Type manually outlook.com and enter your email and last known password.
If you're lucky it was just your browser hijacked and got only the classic scare, reformat the PC and don't use windows anymore. Chance less than < 5%.
Usually the cracker will change your password, remove or modify the recovery email and phone number, but if you're a lucky person, request a password change code to be sent to your phone or recovery email if this is not taken over as well. Chance less than 35%
If these are gone as well (chance more than 95%), than you have to contact Microsoft support, usually the complaints of non-paying are ignored, but my maybe you'll be lucky and they help you recover your account, if not, install Linux get a new mail, enable 2-factor authentication, and take it as a lesson for the future. Don't forget to cancel all your card used online and change all your passwords as well.
Best of luck, because you will need it,
DC1MC