If not detectable, how tnb can even noticed it and estimate the loss?

Provided that if the precise date when the meter was tampered or
damaged or when the supply line, apparatus or system was tampered,
altered or adjusted could not be ascertained by the licensee, the
amount of that loss shall not exceed five times the total amount of
energy, that is estimated by the licensee to have been lost or
dishonestly abstracted or consumed by the consumer, for a period of
thirty-six months prior to the date of discovery of the acts referred to
in paragraphs (a) and (b).

How u find out?

I paranoid my tenant do bitcoin farming. Although electricity is under their name but tnb will still fuck me anyway because they could.

I say the real idiot could be TNB. it is clearly a design issue.
this is how the Sarawak Energy (similar to TNB) works:
1. you abuse electricity too much.
2. SE come to your house and take away a "fuse" at the meter.
3. you buy a "fuse" and reinstall.
4. step 2 and 3 repeat.
5. you already profit enough.
6. repeat

the tenants did not steal, they just don't pay for the electricity