Bad / No service and a ridiculous system

I tried changing a flight booking (numerous times) both on the Mango website and on the App, neither of which worked. I then tried calling the Call Centre as there was a Mango Happy Day sale on and I wanted to make the change. I waited for about an hour and there was still no answer. I tried a few times to no avail. I tried again the next day and finally got through to someone. I was told that the booking could not be changed online. I said that I wanted to pay the online change of booking fee as it was through no fault of mine that I could not use the website or App and I shouldn't be penalised for that. I was then put through to a manager but of course no one answered the call. The service I experienced was absolutely ridiculous and not only am I expected to pay a higher change of booking fee, but I may also have to pay a higher flight price because the sale is over.