I trust that the ban did not arise from offense committed by yourself!
Theoretically, because a MAC address is burned into the adapter, MAC addresses cannot be changed but depending on the card it may be possible using one a number of approaches. The simplest way, if your card supports it, is to change it through the adapter properties in network and sharing section of control panel. There is a good guide here:
How to Change a MAC Address
At the very worst you can simply buy another adapter - they are extremely cheap.