Fee for booking+fee for cancellation for a unvalid ticket

I had to book a flight ticket Between Kaohsiung (Taiwan) and Luxemburg (Europe). On the beginning, it has been quite easy to do it through Skyscanner which used Hop2 and even if Hop2 charged the ticket of a "agent fee" of 32 USD, which is already a bit disappointing, it was still ok and i thought that it was actually a good "travel agent". But for a reason of problem with the VISA of my girlfriend, we had to cancel the flight ticket of my GF. In the same time i decided to modify my flight ticket for the schedule as i had to travel alone and also i decided to upgrade my flight ticket to business class. So we first asked to hop2 how to proceed and what this would cost as we were expecting cancellation fee (which in a normal case would be understandable). They informed us that the cancellation fee would be 100 USD per ticket if we want to cancel, 100 USD for schedule modification and no possibility to upgrade the flight ticket. Due to this information not convenient for me, i decided to use the normal travel agent that my company works with. I also asked them if they could cancel the previous flight tickets for fewer fees. The next day, the normal travel agent contacted me to inform me that they could not cancel it for less fee, but furthermore, my flight ticket for the way back which had and itinerary Luxemburg to Zurich (Saturday), Zurich to Bangkok (Saturday), Bangkok to Kaohsiung (Sunday), was not valid due to the fact that there was no flight Bangkok to Kaohsiung on Sunday because China Airlines has a flight Bangkok to Kaohsiung only on Tuesday, Wednesday, Friday and Saturday.
This means that if we did not cancel (luckily or unluckily) we would have faced big troubles to find our way back home.
When I informed Hop2 of that issue that they obviously did not detect, they said that it was not their fault but China Airlines that changed their flight schedules. Well according to the normal flight agent, it was already a long time that China Airlines changed their schedules and even without taking this in account, it is absolutely the responsibility of Hop2 to avoid this kind of trouble. They just ran away from the problem and say that even if the cancellation fee of the flight company (China Airlines) was waived; the cancellation fee of Hop2 was still 50USD per ticket which means 100USD in total. What was true in this??? I have no idea...
Tired to discuss about that i have accepted and paid the fee...

In resume, Hop2 apply booking fee, Hop2 apply cancellation fee and Hop2 doesn't take the smallest responsibility if anything happens. This means that only by luck i have avoided a very unpleasant journey and i still had to pay 132USD for a terrible service. Moreover, i will never know what is true and what is not true about these cancellation fee which passed from 100USD per ticket to 50USD per ticket (exactly half), this is very strange and smell the dishonesty

In conclusion, I will never use that kind of travel agent anymore. For the direct flights I will check directly on the airlines companies’ web-site and for the more complicate flight I will ask a normal travel agent with who it is much easier and much more convenient for the same fee at the end.