Cards Printed Way. Way Darker than Proof (Nearly Black)

I printed my cards at 4colorprint.com (silkcards.com) with a background color of:

C: 100% M: 78% Y: 45% K: 42%

I received them back and they are nearly black, even darker than navy blue. I realize that an image is not an accurate representation, but it printed out about 8% Black instead of the original 29%.

I understand uploading a photo isn't a good representation, but I can tell you that the color is about 8-9% black. Here is the proof on the right and my received card on the left:

https://imgur.com/a/pc5pAz4

I realize there are deviations in going fro RGB to CMYK, but 20 percent?? They say they will not reprint the cards, and if everyone here agrees that they are right, I will accept defeat. But I am shocked at the final product.

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted January 30, 2019 at 10:01AM by strangeattractors http://bit.ly/2WqVflw