Hi @IonutM, welcome! This is the sms for the transfer of your phone number (numerbehoud)? You receive an sms from us on the number you want to take with you to us. And you have to respond from that same number, otherwise it won't work.

Make sure that the phone you are trying to send the sms from is connected to a mobile network. And that is has enough texts/balance left to send the sms. You have seven days to respond to the sms, so you can try again.

If it continues to not work, we can use another way of validating, for that we need your customer number of your current provider. You can usually find this on your invoice, or in your personal digital environment.

I received the transfer sms yesterday from kpn , today again, but I can't send the sms

I want to mention that the number I want to keep is PrePay  for the last provider not  abonnement end my 

current provider Is Lyca Mobile

I solved it myself, this is the solution for Lyca:
If ou still can’t send/receive SMS please check the Message Centre Number (MCN) in your SMS settings – it should be +31684000111 for Lyca Mobile Netherlands. If you see a different number, enter +31684000111 and turn your handset off and on and re-try sending any unsent SMS. If the problem remains please contact .Thank you from tomorrow I will be a kpn customer:)

Excellent! Good to hear you got it solved, @IonutM, and for sharing your solution. And welcome to KPN