Recover whatsapp data not backed up fully in iCloud

Just changed my iphone6 plus to iPhoneX and transferred content from iCloud. The WhatsApp data was not a recent one in iCloud so in my iphoneX messages that are 6 months old are appearing.

Opening the whatsapp application in iphone 6, it says that the number is already in use in a different phone and asks me to link with a new phone number. I did not do it fearing that it will erase all data linked to my earlier number. so now the WhatsApp is still installed in iPhone 6 but without any WhatsApp account.

I have checked the iphone6 memory and it shows 13 GB storage space usage which means that the messages are still there but not directly accessible. I am also hesitant to sync my iPhone 6 with iTunes fearing it may delete the messages while synchronising.

Is there any way i can retrieve this data ?