re: "I need to report a freelancer, who did not stick to the agreement we made on Upwork."
Actually... You are not required to report a freelancer.
As a client, you may close contracts and stop working with freelancers whenever you want to. For any reason. Or for no reason at all.
As a client, you may manage your projects and the freelancers you hire as you see fit.
Generally speaking, "reporting a freelancer for not sticking to an agreement" is:
- not really a thing on Upwork
- provides no benefit to you
- is not an action for which a specific client-side user interface element is provided.
The best way to do what you are suggesting is to simply include this fact in the feedback you provide when you close the contract. You may end the contract and leave truthful written feedback which states that the freelancer did not stick to the agreement.
If you do that, it is even more powerful than "contacting Upwork Customer Service" and "reporting" the freelancer. Nobody will ever read that report that you provide to Customer Service. But if you report the facts in feedback, any client who considers hiring the freelancer is likely to read what you wrote.