There is an online form to cancel your subscription.

See https://www.kpn.com/service/administratie/opzeggen/opzegging-doorgeven.htm

Unfortunately it is in Dutch but Google translate is quite good nowadays. 

i have filled the form. Unfortunately its not taking my UK number.

Dont know how they can contact me

Let's wait for a KPN moderator to respond as I am, just like you, a customer of KPN and member of this forum.

Hello @prakash , welcome to our forum. The page @wjb sent is for general use when cancelling a subscription.
However when moving out of the country there is a special page to cancel your subscription.
You can fill in the data on www.kpn.com/emigreren. Your subscription will be terminated within 5 working days. 
If you'd like to discuss this by phone you can reach us on 0031612001200 from the UK

P.s I took the liberty of changing your username because it contained your customer number and this is private information. I added it to your private profile.

Good morning @prakash, did you manage to reach my colleagues yet?

I'm assuming you have spoken to them. If you have any other questions. Don't hesitate to ask!