I have an unded contract.
I have finished the work!
And, The last milestone was approved automatically by upwork.
Contacted the client several times to end the contract and leave the feedback.
BUT, I didn't hear from him. Even, if i saw him online.
What's your advice ?
I already contact upwork support to contact him
Mohammed, my advice is do nothing. I think you went too far already asking support to contact him, and really I think it would be better for you if support didn't contact him. If the open contract bothers you, close it yourself. It's not the client's fault that Upwork can lower your Job Success because of contracts without feedback, and if you keep bothering him to leave feedback, he might take offense and leave you poor feedback.