Unable to Ininstall Sophos Endpoint Client on Server 2012 R2

Hi. We have several Windows Server 2012 R2 servers that have a last active date of August 2020 on the Sophos Central Console. I have tried the following in order to uninstall then reinstall the client:

1. Tried to disable tamper protection both on the servers themselves and on Sophos Central - I get an incorrect password error
2. Tried to disable tamper protection from within the Windows Registry - I get an error saying I cannot do that
3. Tried to reset the MCS Agent service but there is no option to either start/stop/delete
4. Rebooting the server as it said to do on the Endpoint client - no luck

I'm not sure what to try next. I've seen recommendations for signing into safe mode but this doesn't appear to work either.

Any advice much appreciated!