One of our customers' upstream provider (AS21548) has been hijacking a prefix for a long time now, making it impossible to use this prefix properly

https://bgp.he.net/ip/23.154.208.0 

We tried support tickets, contacting Aptum/Beanfield's NOC, an abuse request. No reply at all, the tickets just get ignored or closed.

Any help would be appreciated

Regards,