Seasons Greetings RootsChatters

I have been trying without success to find the birth registration for my gg grandfather Thomas Watts
He was born in Bittadon c1841, parents Joseph & Elizabeth Watts
I have him in every census 1841-1901
I have his marriage certificate
But I can't find his birth certificate, which I need to confirm his mother's maiden name as there are a couple of candidates.

There are a few likely births:
Jun Q 1839 Barnstaple 10 40
Dec Q 1842 Barnstaple 10 39
Dec Q 1842 Barnstaple 10 35
But when I tried to order the certificate, the GRO advised that none of them had a father Joseph.

Any suggestions?
Thanks, Jane