re: "i have submitted my work but client is not responding"
Clients are not obligated to respond.
As freelancers, we get paid AUTOMATICALLY.
It does not matter whether or not the client responds.
[As long as we are using Upwork correctly, of course. Are you using it correctly?]
If your client disappears and stops responding, make sure you click to request that the milestone / payment be made. BUT only request it once. If you request multiple times, Upwork goes with the most recent request. I've had to do this in the past, and if the client doesn't respond (and the money is in escrow), Upwork will release the payment to you in 14 days.
If the client has simply stopped responding but the milestone was funded in escrow. Then the client has a period of 14 days (12 more days in this case) from the most recent work submission on a milestone to review and request any changes. After which the funds will automatically be released from escrow to you.
You can have a look at this article about Fixed-Price Protection for more information. Please make sure not to use the Resubmit button again in order to avoid resetting the count-down timer.