Restore WhatsApp chats. iTunes backup.

I just changed my phone from an iPhone4 to an iPhone6, and I have some problems restoring the WhatsApp conversations. I first used an iCloud backup but I realized that backup was made a long time ago so I just lost a lot of chats. Then I made a backup of my old phone on iTunes and restored the new one. All settings, photos, apps, etc were restored but the WhatsApp chats. I can just recover the conversations on the iCloud backup and not the ones from iTunes...
I think I tried everything, I deleted WhatsApp and downloaded it again and it just gives me the option of restoring the chats from iCloud...

Please if someone could help me

PS: sorry if my english is not good, i'm from Spain