The real svchost.exe is a vital part of the OS, that is why a virus might use that name. And there are many different types of viruses, the worst being rootkits because they slip in as part of the OS and embed themselves extremely well. Once imbedded the best designed of them then hide themselves from detection and could be why Malwarebytes cannot see it.
TDSSKiller is designed to do its best to remove the rootkits but there are new viruses invented every day. Nobody can guarantee they remove every virus. That is why it is best to use a combination of tools: booting in safe mode keeps many services from being loaded, so with luck the compromised service doesn't start up. When a service or program is running it is "In Use" and much harder to remove because it must first be stopped. TDSSKiller is designed to find those bad services and remove them so they don't start. RKill is designed to stop any actively running programs that are often used to mask (hide) or restart the virus programs. And then anti-virus software can hopefully remove the programs.
Many businesses charge lots of money to remove viruses because they can be very complicated and quite persistent; it may be something you need to consider if it constantly returns.
Often the best course of action is to back up all your data to an external hard drive and then disconnect it. Then format your computer and completely reinstall windows 7 and all your software including a good anti-virus program, reconnect the external hard drive, and completely scan your back-up for viruses. Finally restore your data. It is often after this time-consuming process that victims realize they should have been backing up their data regularly.
So what I am suggesting is that you boot to safe mode, run TDSSKiller, run RKill, and run Malwarebytes (or another A/V), then boot up to an original W7 OS disk and do a repair install. Next back up all your data to an external hard drive. And if the virus continues to come back you may need to format and reinstall the OS and software or have it looked at by a professional and pay them to do it.