I've seen accounts blocked by IP address because you made too many attempts to connect in too short of time, and the system assumes this is a denial of service (DoS) attack. If you are still blocked, you need to open a support ticket (by email if necessary) and get your IP address unblocked.
I have no idea why you can't change from PHP 5.6 to 7.1. Did you remember to select the domain(s) and press the "Apply" button after selecting the new version? If you have malware in your Wordpress installation, I'm surprised it would let you go back to PHP 5.6 after you tried to go to PHP 7.1. If you tried going to PHP 7.2, try 7.1 instead. 7.2 is much stricter about language conformance and may not work with your version of Wordpress. Maybe it's seeing PHP errors at 7.2, and assuming that there's malware.
If none of that works, you'll have to open another ticket and work with support to find what's wrong with your Wordpress installation. If it really does have malware in it (I don't know how you would test for it, or how they're testing it) you might have to erase all the files and copy in a fresh version of the files. Find out how to do this without wiping out your database (and back up your database first, just to be sure, and know how to restore it) -- it's probably not a normal "installation" of Wordpress, since that will probably clear out your database.
I hope you are familiar with Wordpress support forums (at wordpress.org), as you probably should be looking there for information (if you aren't already).