Tata Photon Plus — Miscommunication by Sales person

I asked for a home demo on Tata photon plus.

person who gave me the demo gave me a receit mentioning a 500 + 200 plan.
he didn't informed me that addon plan of 200 will not be active on basic plan of 500.

now my bill is 1510. I asked their customer care to reduce it according to what has been told to me by your sales person.

but they say that on their records only basic plan of 500 is mentioned
please suggest what can i do.