As your business evolves to succeed the demands on the network will change - they almost always do - you need to keep an eye on how the network is delivering against SLA and expectations.
It is important that change management processes are defined at the outset and that they are followed appropriately. There are generally two kinds of change - planned and unplanned.
Perhaps the supplier has some new capabilities - unless you hold regular reviews these may not be known about.
CN21 can help define an appropriate meeting structure and assist at these meetings.