Demanding money forcefully for cylinder delivery

We order gas from hp ( vinay enterprises - Bangalore ) . They don't give proper change and keep the rest of the money as a tip . Once he took 55rs away from my mother without her consent and I got it back after complaining . Even after complaint raised they doesn't seem to be learning their lesson and when he came recently he ask 40 rs extra than the bill amount .even their agency doesn't provide proper guidance to their employees . sometimes they even say to come and collect . I want to take strict action against them so that they won't do this to any other person . How can I take this legally . I tried sending mail to Bangalore police but they don't respond . Please help me out . I'm tired of these corrupt criminals .