Can you please let us know who else we can contact with this matter?

Is the above correct?

No. I don't think it is right. You should use whom instead. There is a rule for finding this out. Try to answer this question and if you get answer as 'he/she' then 'who' will be used and if the answer is 'him/her' then 'whom' will be used. In the question you mentioned a possible answer can be for example: You can contact him/her.
So since 'him/her' is the answer 'whom' will be used.
Hope this helped.
To learn in detail you can check this link
http://www.wikihow.com/Use-%22Who%22-and-%22Whom%22-Correctly