Apple care plus plan

Trying to follow your post. Are you saying you had the back glass replaced on your iPhone somewhere other than Apple or an actual Apple Authorized Service Provider? If you did, you have likely invalidated your AppleCare+ Plan as Apple won't touch an iPhone which has been tampered with by anyone other than Apple or an Apple Authorized Service Provider.

If this is not your question, please provide more details.

If you had the phone repaired by an unauthorized repair shop, your AppleCare+ plan has been voided. Apple won’t touch it now that it’s been tampered with.

If you had AppleCare+, why in the world did you not take it to Apple or an authorized service provider for repair?

If your situation isn't covered, you'll pay a fee. If the issue with your iPhone is ineligible for service, you may pay the full replacement value.

iPhone Repair and Service - Apple Support (IN)