After checking in 90 minutes before my flight from Tokyo, the immigration held me for 2 hours to fix some paper work, and I missed my flight home. Immigration had me then change my ticket on Delta for the next one and I paid $2k for the change. Original ticket was around $1k. So total is $3k.

I called Delta multiple time, but they refused to refund any of the extra $2k paid.

  What will be the best way to get refund for the extra amount paid  ?

It is not fair for Delta to take advantage of this situation to make this unreasonable amount of profit.

After checking in 90 minutes before my flight from Tokyo, the immigration held me for 2 hours to fix some paperwork, and I missed my flight home. Immigration had me then change my ticket on Delta for the next one and I paid $2k for the change. The original ticket was around $1k. So total is $3k.

I called Delta multiple times, but they refused to refund any of the extra $2k paid. What will be the best way to get refund for the extra amount paid?

It is not fair for Delta to take advantage of this situation to make this unreasonable amount of profit.