You can check your cert using
certbot certificates
It's possible Apache 2.2 does not support ECDSA certs which are the current default from Certbot. You may need to force issuance of an RSA cert (see link below).
Still, that error sounds like it just can't find any kind of cert.
Certbot force RSA with --key-type
https://eff-certbot.readthedocs.io/en/latest/using.html#rsa-and-ecdsa-keys