Hi @TymonCz
A bank transfer to pay an outstanding invoice with KPN has a processing time of 3 working days.
If you had paid via iDeal, it would have been processed the same day.
So if you have used the correct IBAN account number from KPN, along with the requested information, you will be fine.
The email you subsequently received that the payment has failed is probably a reminder email from KPN, which has crossed your payment.
But if you want more certainty, which I can understand, you should really call the telephone customer service via 0800-0402, this has been KPN's telephone number for years and can also be called.
After the voice response has asked you what you are calling for, say the following: payments and invoicing.
And you will then be transferred to the correct department.
The telephone customer service is available Monday to Friday from 8:00 AM to 6:00 PM and on Saturday from 8:00 AM to 5:00 PM.
(Closed on Sundays and public holidays)