If you still have the old dongle it should have the same conditions ie You only have to connect every 180 days to keep credit. New dongles with 30 day expiry came in December 2009.
See here -
Vodafone new dongle
You could try eBay for a pre December 2009 dongle?
Plusnet Plusnet Pro 21CN Netgear DGND3300v2 router
Windows XP Pro SP3