Webrquest proxy credentials

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VB

I would like to get help on how to connect httprequest with proxy string and user: pass.
I bought proxyrack.com residential proxies and they gave me something like this instead of classic IP auth.

premium.residential.proxyrack.net:7000

and then I have username and pass

What I have tried:

Dim myProxy As New WebProxy("https://premium.residential.proxyrack.net:7000")
   myProxy.BypassProxyOnLocal = False
  myProxy.Credentials = New NetworkCredential("username", "password")

I tried also:

WebProxy("premium.residential.proxyrack.net:7000")

but in debug it shows no proxy and no user or pass

thank you for your help.