DKIM thread length of 768 can't update

Hi all,

I recently acquired a new VPS and migrated an old cpanel shard hosting account accross to the new server. I've enabled DKIM and the key length is 768. I'm using BIND and was told over at the feautres request forum that the default now is 2048.
I've tried all sorts to figure out how to increase the key length or generate a new key to use all without success. The raw DKIM key offered up in the cpanel under email authentication is always the old key value.

I've tried disabling the DKIM and renabling.
I've tried creating a new key using ssh openssl following these instructions https://en.wikibooks.org/wiki/Cryptography/Generate_a_keypair_using_OpenSSL and pasting the new public and private keys over those stored in /var/cpanel/domain_keys
I've tried deleting the keys and restarting exim / dns server

I've asked around and spent a few hours googling this and having no luck. I think it might have something to do with the migrated account but I don't know enough to find a workaround?

Could anyone give me a push in the right direction please?