Opodo complaint: Failure of informing about change in the flight

We travelled from Budapest (Hungary) to Phuket Island (Thailand) on the 2nd of August. Unfortunately, our return flight (17th of August) was rescheduled to the 19th, but we were not informed about this change at any time, we learnt about it only informally from the staff of the airports. We were forced to prolong our stay in Thailand, which resulted in not only increased accommodation and transport rental-derived expenses, but we also had to undergo an additional PCR testing that would have been unnecessary if we could fly on the 17th of August, as originally planned.
Beyond the very much increased expenses, we were forced to spend a long time to find formal information regarding our flight. Additionally, we were charged with serious phone bills in because of the distance calls we were forced to make to clarify our flight date.
Firstly, we turned to Opodo, the travel agency, through which we booked this flight, but they asked us to turn to Qatar Airways directly as the airline did not inform Opodo regarding the change of our flight. However, it became clear after exchanging emails with Qatar Airways that it was not true, Qatar Airways informed Opodo about the change automatically but it was Opodo, who failed to process this information.