Could you please unblock the Freeserve mail servers and come to some agreement with Wanadoo about how to effectively stop spammers hosting with Freeserve.
It can not be reasonable the the 2.6 million UK customers of Freeserve, the biggest UK ISP, are all prevented from communicating with any of your customers becasue of the actions of a few hundred spammers.
You should know that Spamhuas have unblocked the Freeserve mail servers after about 2 weeks of prohibition, which is a reasonable approach to deter spammers but allow legitimate usage. The SpamCop block seem to be permanent which really is cracking an acorn with an inductrial pile-driver.
Trust you can sort this one out amicably with Wanadoo (and quickly please).