Redbus — Change in seat

I booked a ticket from Thanjavur to Kumbakonam via red bus where I booked a window seat of no.14, but automatically the seat has been shifted no.5 which is non window, then what is the use of booking via online & selecting the seat on our choice? When enquire about this to the one of the bus authorities, the answer which he gave was to get into the bus in a very rude manner... And the time of 10.30, I was left with no other option rather to travel! Truly a bizarre experience.. if this will continue, kindly inform before hand, so that I will not book the tickets via redbus.. thank you