If you want to permanently delete your account and no longer need to use your current MailChimp account, you can follow the steps below,
Note: After an account is deleted, it can’t be restored. This means all account data, including lists and reports, is removed and can’t be recovered.
Step 1: Login to your account and choose the Account menu.
Step 2: Click the Settings drop-down menu, and choose Pause or delete account.
Step 3: Click Permanently delete this account, and click Continue.
Step 4: Answer the questions provided, and click Permanently Delete Account.
Step 5: In the Confirm Account Deletion pop-up modal, type DELETE and click Delete Your Account to permanently close your MailChimp account.
Once the account is deleted it will display a success message to let you know your account has been closed.