I had my interview at O2 last year. was told I got the job about 30 minutes later. It is a really good company and there are so many benefits so I hope you get the Job.
for your presentation you need to show that your passionate about what your talking about and not just talk about it. I didn't do a presentation for mine I just spoke about it. before the interview as well I checked the website and found out some information about the company. They had recycling policies and a lot of things going on so I just blabbed about them. You will be working around technology so you need to be good with computers.
you need to be organized, a fast thinker and a team player so you need to tell them about all of that. you will be asked about a time when you worked in a team. you just need to emphasis what you did when working in the team.
you will most likely be interviewed by a manager and an assistant manager. mine was with my manager. the trick is to be your self. smile a lot. talk about previous experience and the most important of all, tell them you are passionate about customer service.
don't look at the screen a lot when your doing your presentation. make eye contact and look confident. get there at least 5 minutes early. write down the important stuff on a card so you can look at during the interview to remind you of important things that you don't want to forget
Hope this helps.