[anti-abuse-wg] Abuse Report ignored. What to do as next?

Hello,

the IP 80.94.95.181 is endlessly (ie. brute-force) trying
to hack our emailserver by attempting to login as a user.
The login attempts of course fail, and we have blocked
that IP in the firewall.

But this IP still continues sending packets to our server,
eventhough his packets get dropped/rejected by our firewall.
This now of course constitutes a DoS attack.

10 days ago we filed an Abuse Report to the abuse address
given in the WHOIS database for this IP:
% Abuse contact for '80.94.95.0 - 80.94.95.255' is 
'internethosting-ltd at yandex.ru'

But this hoster seems to ignore all Abuse Reports,
b/c researching this IP on the web shows that
it's a well known abuser IP and many people have
reported and complained about this IP. For example see this:
https://www.abuseipdb.com/check/80.94.95.181

So, what to do if the hoster is uncooperative, like in this case?
Where else to complain, what else to do?

Thx

U.Mutlu
admin & hostmaster