DNS still resolving to old IP address for www but non-www working fine?

Now the non-www record is triggering an SSL error. Upon further investigation, it looks as though the previously delegated CNAME is interferring with the newly delegated values;

NET::ERR_CERT_COMMON_NAME_INVALID

Subject: secure.pageserve.co <<— OLD CNAME AT PREVIOUS NS

Issuer: Let’s Encrypt Authority X3

Expires on: 16 Jan 2019

Current date: 15 Nov 2018