how can i erase my information on my apple device when its lost and they managed to remove my device on my icloud

“They” couldn’t have removed the device from iCloud without your help, although certainly unintentionally. Most likely, you fell for a common phishing scam: You got a text or email from “Apple” or “Apple Security” (or sometimes “Police”) saying your phone has been found and to click on a link to see its location. This is NEVER from Apple or from law enforcement; it is from the thief or fence to steal your Apple ID and identity. Delete any such message without responding to it. Apple never gets involved in lost or stolen devices→Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams

Not only did they remove Activation Lock, they had access to all of the information you saved to iCloud, so take whatever steps are prudent given that any personal information in iCloud was compromised.

bheki258 wrote:

how can i erase my information on my apple device when its lost and they managed to remove my device on my icloud

You don't.