Tamil Nadu State Transport Corporation [TNSTC] — luggage charges non standard

I am travelling in bus no 221 from central to kelambakkam... I am carrying a mini trolley bag which will fit in the cabin and less than 4 kgs... He charged a luggage charges from me. I am travelling with this bag every month for the last 2 years and no one asked for luggage charges. He has collected the money and also very rude to the passengers. Do you have any specific description in the bus which consider as luggage and which are not. Travel date 15th march 2019. Cdj0009 tn-01n-9789.
I am ready to pay for luggage charges provided it is standard for all the buses and specifics are given inside the bus. One bus charging and another do not is not correct.