I can’t help finding the whole “trying to find a way to get out of paying for something I have the benefit of” a bit distasteful. There’s been an admin error at Canyon, that’s all. The admin error doesn’t remove your ethical (and I think legal) obligation to do the right thing and pay for the bike you have had, rather than try to wriggle out of it.
Drop them a line, attach original invoice, I’d suggest the following:
“Thanks for your invoice – I hadn’t noticed the payment hasn’t gone. I’ve reattached the original order confirmation at €XXXX. As this is clearly an innocent admin error on both our parts, I’d proposed splitting the original balance over 4 instalments of €XXXX, payable on the first of each month, starting XX/XX/XX”
Simple. Do the right thing.