Often these scammers use services that provide temporary numbers or even Telegram accounts, and after a period of time they sell them or the service provider sells them, and a third party may buy them. Therefore, this third party does not necessarily have to be a scammer, but it is better not to deal with any account on Telegram without using escrow.
Back to your story, did they pay you the remaining $4,000, or did the project stop, or what?
They paid $2,500. I did half the job as we agreed. I'd have completed it if they paid the balance of $1,500.