I will contact an advisor what the best condition is to do.

For the moment, i've placed a nofollow tag on it, because the contract doensn't say i can't do that. The advertisers are mailed yesterday to inform them that we placed a nofollow tag and that we don't break the contract because nothing is mentioned about that, but i am waiting on their answer.

i will see what they say and we can maybe agree a partial return of the money.
Thanks for the advice

karel