Abuse contact for 121.254.168.0 - 121.254.169.255 is security[at]kidc.net

[C2H5OH]

IPv4 Address : 121.254.128.0 - 121.254.255.255

[ Network Abuse Contact Information ]
Name : Network Abuse
Phone : +82-2-2086-2878
E-Mail : security[at]kidc.net

The subset of this range (where my spam came from - 121.254.168.205);

IPv4 Address : 121.254.168.0 - 121.254.169.255

[ Technical Contact Information ]
Name : IP manager
Organization Name : GABIA Co., Ltd.
Address : 1423-1 KIDC B/D, Seocho-dong, Seocho-gu, SEOUL
Zip Code : 137-070
Phone : +82-2-3473-3901
E-Mail : security[at]gabia.com

Don't know whether security[at]gabia.com might be a more appropriate abuse reporting address for this guilty subset...

[patti2]

Don't know whether security[at]gabia.com might be a more appropriate abuse reporting address for this guilty subset...

KIDC is the upstream ISP and Gabia seems to be the provider for the smaller subnet.

You should probably try to send reports to gabia and escalate to kidc if they don't care.