They already run an official website with support from separate vendors for the web hosting and domain registration.
They want this new webpage designed and linked to their main website. Is there any way i can achieve this?
Sounds like you’ll want to connect your Wix site to an external subdomain. 
I am thinking of doing the same. design a wix site and connect it to an external sub- domain. But i have one small little doubt that i need to clear before o proceed with the client. Can i connect it to a country level/code subdomain such as blog.comoany.bt ??
That, I’m not sure of! Reach out to our dedicated support team via your Partner Dashboard, they should be able to steer you in the right direction.
Will do that! Thank you!