If you have not used your mobile broadband dongle for six months, the SIM would have been cancelled and the number will now have been recycled.
You could try topping up the PAYG dongle, if it accepts the top up, it may reactivate the SIM.
Vodafone do not provide mobile broadband SIMs, they come with the dongle as part of the package.
You would need to purchase a new dongle to begin using the service again.