Network Problem

Good day nullbyters, please Ireally need your help. My question goes thus

Where I live there is this ISP who also provides internet services via cyber cafés. Some months ago, whenever i requested the arp tables on the network (here am seated on a computer at the cyber cafe of the said ISP) it provided me as it is supposed to with valuable info on the network's devices. I say valuable because, whenever I spoofed the MAC of one of the devices on this network (at ip address 192.168.0.10 with MAC been 00121247... (in all of its cyber cafes), which I later after some recon. found out to be manufactured by a certain PLUS Corporation) I instantly found I had free internet (i bypassed their captive portal in other words, since authentication is done via a captive portal). not only that, I was able to download at the maximum speed provided by the ISP, which is about 8Mbps when on IDM. Whenever i went to another cyber still owned by the said ISP, all was the same, spoofing MAC of device at ip 192.168.0.10 with MAC having at least 00121247... (the last 2 or 4 digits of the MAC changed with different cyber cafés). I thus decided to inform the network personel but did not give them all the details cause I really wanted a pay, but thinking they were wise they went and did what I don't know till date, that's why am here. Now whenever i do an arp scan, device 192.168.0.10 almost never shows up except maybe when i use say advanced ip scanner, and even when it does, it has afake MAC (there a so many duplicate MACs on the network right now, almost all devices bare the captive portal's MAC. That not withstanding, I crammed the MAC and whenever i spoof it, free internet returns but now what I want is what did they do on the network, can I still view those MACs. Thanks in advance.