iCloud Wont back up Whatsapp

So I am upgrading from an iPhone 5s to and iPhone 6s both with up to date iOS's and want to transfer across my Whatsapp. I can see a Whatsapp back up on my iCloud but when I try to restore it on the new phone it does not recognise it! I have tried doing a manual back up but this doesn't work it just freezes at 0%. I have contacted Whatsapp and they say I need to delete the old Whatsapp back up and try again, but the iCloud won't actually let me click on it to delete it. I have tried logging in to iCloud on my PC (Google Chrome on Windows 10 and also Internet Explorer) but it just say "cannot access this folder at the moment, please try gain later". Please help! I don't want to lose all my messages!