Unsure why you would go to such lengths as to replicate an existing artist and then get pissy when it is credited to the person who you are copying.
Also, why would banksy try and claim it as his own, if it wasn't, not like he needs the attention (he gets it enough with his actual work)
An artist from Bham, who I'd never heard of (itchers) has said it's his handiwork & not a Banksy!