You need to consult with a family law attorney who knows how to handle military benefits properly.
The SBP is an insurance plan that you pay premiums into so that if you die, your spouse and other eligible beneficiaries will have income because your death means your retirement pay will end.
You do not recoup premiums, but if you continued to pay premiums until you reached 70, you would not have to pay any more premiums to receive coverage. This is insurance, not a retirement fund. You pay insurance for coverage on your automobile and say you stop coverage on the auto, you certainly will not recover paid premiums. Same story with the SBP.
Your son probably does not have coverage because he is too old and probably not incapacitated. A POA does not make any difference because the SBP never gave coverage to you.
To prevent the SBP from being screwed up, you need to talk to a competent attorney that knows how to handle SBP coverage in the divorce process.
The short answer is that the premiums are not refunded because the statute specifically states that they cannot be refunded (except, I remember correctly, if the beneficiary passes away very shortly after making an election). We could probably get into a discourse of whether they should or shouldn't be refundable, but I don't think that's what you're looking for.
If you do not have a spouse or dependent child, then you can elect SBP coverage to someone who has an "insurable interest" - and your son probably falls into that category. There may be a limitation on when you can name someone with an "insurable interest" as the beneficiary, but to be honest I would have to research that issue to be certain.
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