Did you make use of the ‘overstapservice’? Then it's quite common to lose connection within one or a couple of days after Ziggo completes their installation and lets KPN know that it has been completed. Nothing can be done to alter this process as it happens fully automated, at least on the side of KPN. Who told you that you would keep your KPN-connection for two weeks after Ziggo installed their equipment?

first of all, I received ZIGGO box just yesterday, and have not installed it yet. ZIGGO told me (and it is clearly written on the box) that I will have 2 weeks with old provider after the box is delivered

But did you use the ‘overstapservice’ with Ziggo?

KPN has been a disaster, at least for me.. really happy I am leaving. 
Today called the support, after 20 minutes waiting, the guy just hung up the phone when heard about my complain. super rude staff

I don't know, I just went to they store and they did it for me. 

Did you have to cancel your subscription at KPN yourself? Because if not then the ‘overstapservice’ was added to the subscription. If this is the case, chances are very likely that Ziggo reported their delivery as complete to KPN which means KPN can end the contract and terminate the connection within the terms of the ‘overstapservice’. The termination of a connection happens fully automated. In that case it's Ziggo who is at fault with either misinformation or for completing the order to early. I can't check their systems so I have no idea.

It could be something else in our network as well, maybe somebody made a mistake and accidentally removed your connection, this can always happen as we are people who do the actual work in the infrastructure and with thousands of connection in a single exchange a mistake is made easily. Only way to find out is by calling 0800-0402 in a calmly matter. 

is there any way to make sure if I call 0800-0402 and waiting for 20 minutes, the person will not hung up the phone on me? I literally did not say a single bad thing… even though I should have

Who says he hung up? Could be a glitch in the communication which ment the call was disconnected. Unfortunately this happens sometimes. You could also fill out your forum profile and a moderator can check on it as well but this will probably be later today, tomorrow or even saturday.

Hi @mhsgoud, I'm sorry to hear that your connection stopped working earlier than expected. Glad to see that @NHendriks already came to your aid. 

What he says is correct: maybe something went wrong - as well with your connection as with the connection when you called our customerservice. Contacting our customerservice is the fastest way to figure out what is going on, our colleagues there will help you right away.