Hi Hollie
I have never done an interview for E.ON specifically but hopefully I can be of assistance. The first question to ask is this:
1) Did the people who got asked technical questions have technical degrees?
Some areas of a business do expect graduates with more vocational knowledge (IT being the obvious one). Legal would also expect candidates with some training in Law. It would make sense then to give them such a grilling. Finance tends to be open to graduates from a wider range of backgrounds (mathematics and physics graduates make excellent candidates by the way and wouldn't necessarily have deep accounting knowledge. Interviewers will almost always ask what you studied on your degree too, even if it is non-relevant (indeed accountancy grads may get more of a grilling, because the interviewer can ask more technical questions)!
The next question is this:
2) Can you prove to them that you want to be an accountant/finance professional?
Here's the problem for recruiters in my profession (I work in banking). At school, kids aren't coached enough about their future careers. They often leave school thinking that there are four 'ultimate' good jobs: lawyer, investment banker, accountant and doctor. For every kid who isn't brilliant at science, they aim for the first three without considering all the equally well paid careers out there. Unsurprisingly these fields are oversubscribed at entry level. However, this is not true at more senior positions (or they would earn less, according to economic theory). Why? The huge drop out rate of course!
So, the most important thing you have to do at interview is to prove you want to be an accountant and aren't just looking for a 'good' career.
So, finally:
3) How can you prove you want to be an accountant?
You're obviously bright, you're a mathematics scholar after all. You may have no training in finance but you'll cope reading a company's annual report. Please go here and read E.ON's last annual report:
http://www.eon.com/en/about-us/publications/annual-report.htmlAlso, read the financial press before your interview. Show some awareness of what is going on, even if you don't understand how it all works.
Finally, think of examples of things you have done in your life to date that might be relevant to accountancy. This might not be obvious; we all pick up skills in the oddest of circumstances after all!