Mistakenly bought game off Xbox store, refund issue

You'll need to contact support and speak to billing. 1-800-4my-xbox if you're in the US/Canada or http://support.xbox.com/contact-us

If you recently just bought the pack i am sure a refund will be possible on whichever account you mistakenly bought it on follow this link for more help https://support.xbox.com/en-US/billing/xbox-subscriptions/digital-goods-subscriptions-refund

Kinda. He was playing the game for about three weeks with the content included before he bought the DLC pack. He’s then continued playing afterwards for a week before I realised, managed to unlock his acount (he’d changed and then forgotten his password) and put in the refund request.

It’s then taken two weeks for Microsoft to respond during which he has played the game - I didn’t see there being an issue since it’s not a refund of the original software, but a refund of a second copy mistakenly bought on the same console.

I forgot that I bought 2 months, and mistakenly did not write it.

Is there a refund policy for 2 months and 3 months?

I have 2 months and am about to get 3 months.

I think you get one refund, per lifetime on games. As least that's what someone at Xbox customer service told me. I got a refund once on some digital gear that was mistakenly charged to my card multiple times.