Opodo review: Charges for flight change

I needed to travel to Germany, but, within 2 hours, had to change the dates. I had just signed up for Opodo Prime service, and was told that there was a charge of around £25 for a change. I was not informed that I would have to buy a new flight, but only pay the different. I tried to do that change online, as I had once done with another airline, to be told that I had to wait for over 24 hours for them to 'decide' that I could change the flight. During my conversation with the woman helping me, she told me prices of flights. I understood that to mean just as I had had in other cirumstances, to pay the difference and the charge. I told her to book the flight and she did but then, I discovered that I had simply been charged for a new flight. I have been in touch with them. They said they listened to the calls, and that I had understood what they were doing. I asked for the calls to be sent to me. They did so - but did not provide a code so that I could listen. I know exactly how much the flights were the moment I wanted to change, and it would not have added up to the amount they charged me. I feel they were obsfucating and were not being clear and honest. I would not have changed the flight had I been given all of that information BEFORE the fact.