You may have a rootkit. Few things get by Malwarebytes Antimalware. Here's what you do:

Download Unhackme from http://greatis.com/unhackme/

Install it, update it, and follow its directions to use it to scan your system.

BTW, you have already installed all available security updates on your system, right? If not, you need to do that also.

Do you have another PC on a network in your home? If you have another PC on a router/switch, then the other PC may also be infected and is reinfecting your PC.

Shout back if you have further trouble. This may need manual removal, which I can do for you if desired.