I agree with blitzstryker...your dates are a little confusing. The original ord dates will be 2 yrs from enlistment date. which is ard jun 2013.
There is a difference when your son sign on during bmt or after bmt. There is a recent scheme where NSF can volunteer to extend the ORD by 6 mths in their current vocation. And if sign on during bmt, it prob means your son is considering a career in the military. Thus there is a contract for some years. Last time it was 6 years, I dun know if it's the same now. The 6 years include the 2 yrs of NS.
You really have to check the contract clauses. I remember last time when I was offered to sign on before bmt, there was a certain sum of money given i think upfront upon signing. Thereafter, even during bmt will be receiving more money than normal recruits. Upon completing vocation course, the pay is then adjusted to the regular pay for that vocation.
Since your son failed the course, it could be because he's been getting salary from the army from the time he's in bmt to the time he's in the course.
Another thing is was he given any chance for recourse? Or there is a period of waiting after failing the course to be posted to another unit. All in all, was he receiving higher pay than normal NSF during the entire period?
It could be becos he taken the regular pay and need to serve more to pay back. Ask your son too talk to his S1 aka HR dept in his unit. Also can try bringing it up during the monthly interview with the PC. Last few resorts, you son call the counselling hotline and say he's depressed...bla bla bla.
Or some people will bring up to MP - may or may not work...