KPN collects subscription fees even after assuring that contract would be cancelled

I made a call to KPN customer service in Feb 2021 to cancel my current internet subscription. I was promised that the connection would continue for a period of 30 days from that call and that I’d be charged one additional month to which we humbly obliged. However, even after 30 days past the date of that call to the customer service we were again charged full subscription fees on 4th April 2021.

I made a call again during the week of 19th April 2021 and I was assured again that the subscription would be cancelled and I would be refunded the entire subscription fees. However, I was again charged on 4th May 2021.

This seems bizarre that KPN keeps charging the fees even after two reminders. As I had already informed KPN to terminate the contract back in Feb I would like to have a full refund of the charges that have been debited from my account in April and in May.