I used this to get banned from alteriwnet once and it only works once sorry if this has already been found though. You need a wireless router and a maybe a modem cable it depends.
Firstly if you were on wirless when you got banned switch to wired using the modem cable. If you were wired unplug and switch to wireless.
Secondly just change your mac address and ip I have O2 so i had to use some telnet commands:
ip ifdetach intf=O2_ADSL2plus
ip ifconfig intf=O2_ADSL2plus hwaddr=02:xx:xx:xx:xx:xx
ip ifattach intf=O2_ADSL2plus
(change the xx's with numbers and letters 0-9 a-f)
But that obviously wont work for everyone. Just search it on google how to change mac address.
Thirdly delete all the alteriwnet folder and if you saved the rar/zip files from when you first downloaded alteriwnet just reinstall everything if you dont download everything again. Run alteriwnet (you will be level 1 sorry) but you can use a trainer.
Hope I help!
PS: try not to get banned again because this only works once.