I performed a withdrawal operation in the browser.
I confirmed the withdrawal with the e-mail after the operation and changed to "In process" state at "pending withdrawals" window.
The withdrawal is not completed even if it passes more than one week with the state of "In process".
I issued a ticket with Yobit.NET support and contacted Yobit, but I have not heard back from it even after more than a week.
What should I do. Can someone please help me?

What is that coin you are trying to withdraw? There's no way that I can help you out with it. And if you had issued a ticket, you had to wait for their reply and get into your query.
Hi, Roommate Agreement.
Thank you for your reply.
Because Yobit's wallet is empty, is it that I can not withdraw?
There is no reply from Yobit, so I can not cancel my withdrawal.
Is there no reply from Yobit's support ticket in the future?
There's a possibility that the wallet is empty for it since it is "in process" but it has been a week so big chance that their wallet on that coin is totally dry.
Just wait for them and hope to refill it soon so your withdrawal will be successful.