You may check for the hosting account details and access to the Plesk from the client area itself.


Steps:


1) Login to your client area 


2) Proceed to  -> Services -> My Services -> Choose the hosting and click on Manage Product and the nameservers details will be shown there. 


By default the nameserver would be:


 ns184.mschosting.com
ns185.mschosting.com
ns186.mschosting.com




Sample as below: