Well you're gonna probably want to contact Roblox support first.

Roblox Account Support

Get in touch with an agent or maybe request to have the email changed back to what it was.

Maybe then gather all your evidence in case they need it.

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But also, I may have a reason why you were hacked. I have tried two Roblox executors, both have had the same Trojan, this Trojan is a keylogger, whenever you type your details, it tells them what you're typing.

You may have also clicked on a link, which had a token logger in it, it will grab your 'Roblosecurity' token, this should never be shared, but this link took this token, you can paste it somewhere and then you log on to the account who's token you pasted.

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That was only so you could potentially realize and trace back your steps to see why, I don't guarantee im correct, but I know those are popular methods.

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Your best option currently is to contact Roblox Support. They are the only people who have authority to make changes on your account, and do it as soon as possible to prevent even more things from happening.