Penalty fee and double contract because of wrong information from KPN

For two years, I had been using internet from the company Ziggo. After renewing my contract with Ziggo, KPN's customer service department contacted me and informed me that I was using Ziggo's cable internet with lower speed and paying a higher price, while they could offer me fiber internet with double the speed at half the price. I explained that my new contract with Ziggo had started just two months ago. However, the KPN representative told me that Ziggo is a subsidiary of KPN, and they could cancel my contract in their system without any issue, allowing me to switch to KPN immediately. A few days later, a KPN representative visited my home and replaced all the equipment.

The following month, I received a letter from Ziggo stating that I had to pay a €980 penalty for terminating the contract early!

I contacted KPN's customer service, explained the issue, and they acknowledged that their representative had falsely communicated this information. They agreed to stop my contract with KPN and return the equipment. However, this month, I received the first invoice for the KPN contract. When I contacted customer service again, they informed me that my contract had not been canceled and was still active, and they could not do anything about it.

Due to this misleading marketing and providing false information, I absolutely will not use KPN's services, and I have already removed all the equipment. Please follow up to ensure that my contract is canceled, as I have already spent enough time and money trying to resolve this issue. If you cannot provide a solution, please direct me to a higher authority where I can file a formal complaint.