I can, in fact, recycle just about as many 'Small Business Surveys' as you care to post to me.   No matter how many you send, it's always going to be quicker and easier for me to fling them straight into the recycling than to open, check figures, tick boxes and put the damn thing back in the post. 

I'm guessing this is also the case for every other small business you are sending these to.  This is why nobody is returning them to you.  Stop!   Instead, perhaps there is an incentive you could spend all that postage money on that might induce small businesses to tell you the stuff you want to know?   An incentive other than 'We will stop sending you surveys' preferably.