To add to what hosemary wrote, if you don't want anyone to be able to access the account anymore, you can "self ban". Xal0lex wrote a step-by-step tutorial on how to do it(which I have shared below) you just need to follow it.
Go to your profile, click on "Account Related Settings" and there you will find the item "Secret Question". Next, enter your question (1), the answer (2), your current password (3) and click "Change profile". That's it, the secret question is set.
Then you log out of your profile and are going to log into the forum again. On the forum login page, click the "Forgot your password?". On the "Password reminder" page, enter your username and check the "Ask me my question" box and click the "Send" button.
Next, here you enter the correct answer to the secret question you set (1), a new password (2) and again a new password for confirmation (3) and click the "Save" button. Yes, you can enter whatever password you want. You won't need it anymore anyway.
Congratulations, you have banned yourself
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Then you log out of your profile and are going to log into the forum again. On the forum login page, click the "Forgot your password?". On the "Password reminder" page, enter your username and check the "Ask me my question" box and click the "Send" button.
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Next, here you enter the correct answer to the secret question you set (1), a new password (2) and again a new password for confirmation (3) and click the "Save" button. Yes, you can enter whatever password you want. You won't need it anymore anyway.
Congratulations, you have banned yourself
But clear things up, having multiple accounts is not allowed in this forum
Is the "not" a typo?18. Having multiple accounts and account sales are allowed, but account sales are discouraged.