iphone retrieving number from whatsapp

I have been sending messages to a contact who changed her number. When i message I usually go to the conversation and continue, assuming it would be sent to the remaining number (new one) on my phone. Instead it would seem to be sending it to the old number. When i press the i for info button it includes her previous number which it says was retrieved from whatsapp, and I think this is why it is sending it incorrectly. I have since texted back to the correct number directly and it works.

Can someone please confirm if I am either going mad or am correct (the consequences of this are driving me mad!!)