I worked for an insurance company for a few months. I requested that commissions be paid on closed business only. They didn't do what I requested and now they say I owe them for a commission. The reason the policy wasn't accepted by the client was because the doubled the premiums on them in underwriting. After they said I owed them the chargeback they continued giving me commissions on other business. As far as I'm concerned there was much more written than was denied. I don't believe their accounting and they wouldn't break it down by client.

... I don't believe their accounting and they wouldn't break it down by client.

Tell them "no tickee, no shirtee". In other words, if they really want you to pay them back they will give you an appropriate accounting. That's what you can insist upon if they were to sue you for it. So perhaps they are not serious about getting this back.