The airline is responsible if anything goes wrong, as you book through them. They should be your point of contact and sort everything out for you. But airlines may employ the airport's special assistance team to support you. The team could be made up of different companies and you may need to speak to several people.
You may be asked to repeat information, even when you provided it in advance. It may help to:
expect a long wait and prepare to be patient
have documents ready, like manuals for mobility equipment
Finding ways to stay calm
Flying can be stressful. You can develop ways of dealing emotionally with travel problems. See what works for you. You could try:
looking at a map of the airport on the website in advance
To make a formal complaint after your journey, start with your airline.
The Civil Aviation Authority website provides a directory of airline websites. This links to information on their special assistance services. You can make a complaint through the airline website or by phone or post if they provide those options.