Hi. Ive had a telephone interview for a Train Manager with GWR recently and considering that you are also applying for a customer services role, I would imagine the interview questions will be very similar.
The interview itself lasts for 25 minutes and to be honest, the questions are fairly generic for a customer services role and there were no surprising questions. It is mostly just the 'Give an example of .... " type questions including the following topics: working in a team; leading a team; a difficult situation (or emergency situation) and how YOU dealt with it; working in customer services; your motivation for the job and your passion for customer services; your ability to influence people; building relationships with colleagues.
Best of Luck for the interview!