Baptism Certificate

Been waiting to have my name to Foreign Births Registration base on my grandfather John Corcoran Baptism of 16-Apr-1851.

They require a birth Certificate but Birth Certificates don't go back that far.  I sent them a Church Baptism Record created by rootsireland.ie but that is not acceptable. They want a statement that a birth certificate is not available which I have applied for and a Baptism Certificate issue by his Parish Church.  Have not heard back from the Church to my email inquire.  I was born when my dad was 60 years old.  Can you recommend a contact person to speak too?  Baptism: 16-Apr-1851, Address: Sonna, Parish: Colmcille, County Longford.    Frank Corcoran icorkman @ gmail.com