Travel Agency Changed The Flight Plan For Onward Journey

I had booked a tour via a travel agency, initially in whatsapp chat with sales agent they had mentioned the flight details which was ok for me, but i can see as it is a group tour, out of 25 travellers 12 are given the same flight and the others are given a connecting flight. Direct flight that was told in the whatsapp chat having 5 hours of direct journey - night 9 pm Connecting flight has total 9 hours of journey - evening 5 pm both in terms of flight duration and flight timing is problamtic to me- now even after raising this to the agency they are not postively responding to this, rather declining to help. moreover they are sighting the terms and conditions, where they have mentioned the exclusion of any airfare increase - now they are saying if you want the same direct flights you can pay extra and do it - they are not looking to help in any way, what can i do, visa is done as well - i dont see options to back down and getting refund will be a long route, what should i do?