TTDC - Not Allotted The Booked Seat Number

We have booked 4 tickets to tirupati in TTDC.we have booked seat no.s 11,12 17 and 18.but they allotted seats in a small van in the last row.we have a small kid with us.the bus jerks in ups and down.It is difficult to travel in the bus sitting in last rows.we called the customer care landline number at 6 a.m.A gents picked up the call and he is asking me to adjust and sit..and he allotted our seat to someone. He is arrogantly speaking to me over the phone.u r ony travelling to temple..why can't u adjust and sit?he is not emphathetic and he is not ready to help us.we spent nearly 7500 for the tickets.why we have to adjust?