I think first thing you should do, is report police. Next you should cut the power supply if it's under your name at TNB -- the charges would have far exceeded your deposit by now. So tell TNB to cut it. Oh and if its under your name you are liable.

How do you know they steal TNB power? If you are so sure, report to TNB and get TNB to take action against them as well (TNB got more lawyers, more fire power).