Devices still obtaining IP address after being filtered by MAC address

I am new to a network and we are currently waiting to move into a new building. However, before we do that we are in an older building with older infrastructure. We are running out of IP's so I have decided to finally force a somewhat ignore policy of not connecting personal mobile devices to the network. I have gone through and started filtering any iphone or andriod devices I see connected by just adding them to the list of filtered MAC addresses. However, they still seem to be able to obtain an IP. Once they are connected to the network they cant actually access the internet or exchange data, but they are able to get an IP address. Any thoughts on why this is or how to prevent them from even being able to get an IP address? Right now I am filtering them on the router (TL-ER6020).