This is the first time that APEM have recruited a cadet pilot so I assume that further cadet recruitment will depend on how well/ badly this recruitment goes and will rely upon further development and growth in their fleet of aircraft and airborne surveillance business. There is a link for a ‘frequently asked questions’ document on the cadet vacancy page, perhaps your query is answered in that document, failing that the document does detail a recruitment email address to send your queries to, not sure if this is the email address that you have already tried with no success.
Failing that, on the left hand side of their web page is link to a team list of all employees with their email details so you could send an email direct to the chief pilot or possibly one of the HR team. I imagine that the answer would be that they don’t know if they’ll recruit further cadets but keep an eye on the vacancies list where future cadet requirements will be listed. The reason I suspect that you will get this answer is that several months ago I contacted their chief pilot directly asking about pilot turnover and short term future requirements and I received a very polite reply inviting me to keep an eye on the vacancies section of their website.