Whatsapp version expired 5 December 2017

Hi.
Since 5 December 2017, every time I turn off the phone, when I turn on, I get the message that the whatsapp version expired 5 December. If I click on update, it tries to open a webpage but nothing happens. However, if I go to Play Store and update whatsapp from there, everything is fixed. Hoewever, whenever I turn off again and turn on the phone, same happens again. In essence, if I turn off the phone everyday, I have to update from play store whatsapp everyday. My android version is 7.0. My phone is Gretel GT6000. I tried to uninstall and install whatsapp, but it didnt solve the problem. Date and time are setup automatically. I wrote to whatsapp but they didnt help at all.
Please, could anybody help me?
Regards

Thanks. The issue is that whatsapp doesnt work, if I dont update it (from play store), so it is not only the message. The problem is real.

James, I have followed your instructions. But, unfortunately, it didnt work. Thanks anyway.