Providing transit to unallocated networks

Hi, I've come across a network which seem to be getting transit yet both the ASN and IP space is not allocated by the RIR. It does appear at some point that it was valid however this is no longer the case. The network is single homed and I tried asking the transit provider what their policy was on this but got no answer. Has anyone seen anything like this? What has happened in the past with things like this? Thanks, Alistair