I have been using Parental Controls to try and limit my sons gaming addiction (PC connected via LAN). It worked for a while, then I noticed he was still gaming after he should have been locked out. I noticed new versions of his PC in the list of connected LAN devices. A quick youtube search showed there are at least two easy ways of getting around the Parental Controls.
From what I can see, there is no way of blocking new MAC adresses over LAN - there is over wifi, but I don't think there is for LAN connections. Am I right? Thanks in advance.
Buy a linksys or tplink and use the rubbish vodafone ULTRA device only to get in from the street (to avoid the BS tier 1 support question "what device are you using") then wan it to a device that has proper functions. For me Linksys very nice interface.
I had the same with WIFI mac fiter not blocking anything.
Was going to attempt Parental Control till I read your issues.