eDreams complaint: Flight change

I booked a flight to Colombia, Medellin for the 1st of June 2022. Due to personal reasons, I contacted Edreams and asked them to change my flight to the 31st July instead. After several calls and chats with them, they found a flight and charged me more than £500 for the difference on the flight change which they ed over the phone all OK. I of course made life arrangements ass I thought my flight was changed. Few days later, I realised my flight wasn’t changed so that I chased them again. I had multiple chats with them as well as phone calls during 3 weeks. Yesterday I called them again and they told me that Avianca, the airline, didn’t have flights for that date and that I had to pay more than £1100 to request another day to fly to Colombia. In fact, I’ve been suffering from stress and depression because of this. Please help claim for my rights.