Thanks all,
I found the solution;
Deleting custom fields does not delete the values that were attached to those fields. This is an intentional move to prevent deleting crucial data after deleting a custom field by mistake. To delete the information attached to the posts, follow the following steps:
1. Recreate the custom fields using similar field names. Ensure they do not have the required setting switched to yes so as to avoid any validation errors.
2. Navigate to the ACF options page.
3. Delete the information and save the options page.
4. Delete the code in your template file which is responsible for displaying this information.
5. Delete the custom fields.
