Returned modem in KPN winkel, but still getting emails to return it

Hello,

I cancelled my contract in December (after I moved out from the house) - when I asked KPN on the phone if they can send me a return box to my new address they said that it's not possible and return box will be sent to the address where internet has been used. After that phone call I decided that the best idea will be to return it to KPN winkel. I did it so at the address: Nieuwe Passage 22, 3111 EG Schiedam. Consultant accepted my router and let me fill my details on computer, so I could receive a confirmation of my return. I received an email at 11th January that my contract has been successfully cancelled, but today I received an email that modem should be returned within 7 days from now on... Can anyone explain to me this situation? I haven't received any confirmation from KPN that router has been returned to them... I don't want to pay any fine as I've done everything correctly! Please help.