Here is what WORKED for us three times whenever we moved within DC area.
Go to their website helpcenter click on CONTACT US. it will bring a dropdown menu where you select "Classified and advertising" which will open a form. Simply fill out the form and in the description, just say: "Please stop marketplace advertisement at the following address: (your address)".
They will fix it within a day or so. You may still get one more copy but that's it. DO provide your email ID so that they generate the ticket and send it to you in case you want to follow up.
https://helpcenter.washingtonpost.com/hc/en-us/requests/new?ticket_form_id=403687
You may also chat with someone on their site but that may take some time.