Prasanna Travels — Bus time changed by operator and provide seat in two seats birth

I book single seat ticket for Amravati to Pune for timing 8.15pm departure for 1850/-.The purple travels send me new bus timings with departure at 6.30 pm with seat in double seat birth. The single birth is expensive than double seat birth, when i check the price for seat they have provided me its showing 1150/- only. The difference of 700/- i gave them for single birth and Premium Bus at 8.15. There are different buses run by purple, the price of 8.15 bus is higher than other buses. They are providing me seat in their normal bus and double seat. I want refund of my 700/- difference because i have option of booking 1150/- seat but i go for 1850/- for comfort, but they are not providing premium bus and single seat.