Ocado question re: substitutions

I wasn't sure where to put this, since it's not exactly a food issue, it's a food procurement issue. 

We regularly order from Ocado, and are generally happy.  But I've noticed that when they don't have a particular item, they often substitute for something else.  I checked on the website and didn't see one, but is there any way to say that you don't want to allow substitutes? 

Sometimes it's not a big deal, it's just something little like green grapes for red.  Not the biggest deal.

But today it matters a bit more -- I was pleased to see that they are stocking Catsan cat litter (not food!).  Great!  So I ordered 2 packages.  But the delivery text tells me that they've substituted something else for it.  Not good.  It's useless to me because my cats won't use anything else.  I'm going to tell the driver to take it off and credit me, but it would be easier for everyone if there was a way to indicate that substitutions aren't acceptable. 

Anyone?

I don't think you can turn off subs, subs are so rare and normally better (oooh £30 bottle of wine instead of £10 and I only pay £10...yay!) so there's no way to turn them off

But yes you can reject your subs from your driver. Annoying in your case though when you know you don't want what they're bringing.

Thanks!  And, yeah, I generally don't mind (or am happy with) the subs.  There are so few times that I am that tied to a specific brand and product. 

Although, if they'd like to give me a £30 bottle of wine instead of £10 of cat litter, I'd be quite happy.