ASN "Hijacked"

Hi Folks, This is a new one for me. One of my AS numbers (AS27421) appears to be being used by someone in Brazil. We haven't seen any actual effects of the hijack -- that is, we don't appear to be losing any traffic. The only reason we noticed is because it's being reported on HE's BGP monitoring site. I've reached out to the abuse contact for the AS's the hijacker is peering with (AS1000, AS271253 - same abuse contact for both) several times and gotten no response. Though, looking at which prefixes AS271253 is originating, it doesn't appear this AS cares much about proper behavior. If anyone has any advice on next steps, it would be appreciated. Thanks, Matt