The starting date of subscription

Dear Reader,

The KPN has been chosen as an internet provider for my house, and the starting date was arranged for December 18th but somehow the starting date of mine was changed because of the current owner's cancellation date of the subscription. 

The current subscription is not my problem, and he has to cancel his subscription before moving as well and he will have done it before my starting date. 

Is it possible to arrange my starting date again otherwise it will be a big problem for me because I work from home by using the Internet?

Furkan Ozdemir