Here is the basic greeting I suggest to call centres who can they customise how they wish:
This is Widgets Ltd. I'm sorry it has not been possible to connect your call at this time. For further information or to opt-out of further communication please ring 0161 000 0000.
Make sure the message is clear and well-spoken. I don't see the need to repeat the number in the message as the customer has the Caller ID to redial should they need to.