Part of the problem is the OP appears not to have asked for anything specific, hence the $200 vouchers which are a fairly typical DL good will gesture. Two pointers in writing these complaints:

1) Be as brief and to the point as possible.
2) Ask for what you want. You won't alway get it, but the odds improve.

My personal opinion is that such displaced pax should be refunded the fare difference in $$ (based on what the pax actually would have paid, e.g. L-U-T if they had been available), plus the good will vouchers.

Good luck in round two.