In order to block wireless users through the mydlink app or website your mydlink router must be registered to a mydlink account.
Step 1: Log into your mydlink account at http://eu.mydlink.com
Step 2: Select your router to bring up the Router Status page
Step 3: Under the Connection List, click on the block button to remove the selected user
Click Apply to confirm the settings.
The selected user will now be blocked from accessing your network/internet and is automatically added to the routers MAC Address Filter.