yes that is what OP needs to do now because actually he is in favor here, 2500$ for half
of the job and the remaining 1500 for the another half , which means he had more than the remaining.
though Maybe OP is just acting towards human nature and not about the money anymore ,
because it is normal to have concern when you think there is something wrong happened and you can help
saving others in situation like this(if there is truly an speculation)
OP's story doesn't look real because it will be difficult for somebody or a client to just give you $2,500 without an escrow. I don't think anyone has such money to waste even billionaires might not make such a mistake. The story is more suspicious because the writer has come up with the same story some time ago. I don't know what he intends to achieve from these stories, maybe he wants people to trust him. But I doubt if he would achieve such an aim by coming up with this kind of story.
If I understood your narration very well, I wouldn't be too warried about who the new person is behind the telegram account. I am more concerned about the deposit that has been made to you. Are you going to inform law enforcement agencies and give them the money so that they can carry out an investigation and where possible trace and return the money to the owner since the job was not done? Just block the new person and the problem is solved. Whenever the old person resurfaces, they can always reach via your telegram handle.
OP said that the $2,500 was an upfront payment for the job and he has done half of it. His option should be to wait until the real client contacts him. And he should be able to verify that it is his original client not just through the telegram platform but through other means.