Prefix hijacking by AS20115

I've got a problem where AS20115 continues to announce prefixes after BGP neighbors were shutdown. They claim it's a wedged BGP process but aren't in any hurry to fix it outside of a maintenance window. I'm at a loss of what else I can do. They admit the problem but won't take action saying it needs to wait for a maintenance window. Am I out of line insisting that's an unacceptable response to a problem that results in prefix/traffic hijacking? ~Seth