Store Credit for WooCommerce

I’ve tried a plug-in that does this, but it crashed my site because it was so big. What I want is below:

Customer spends 0 to 100 = gets store credit coupon for £8 (8% 0f £100) for next purchase
Customer spends 100 to 200 = gets store credit coupon for £18 (9% 0f £200) for next purchase
Customer spends 200 to 300 = gets store credit coupon for £30 (10% 0f £300) for next purchase
Customer spends 300 to 400 = gets store credit coupon for £44 (11% 0f £400) for next purchase
Customer spends 500+ = gets store credit coupon for £60 (12% 0f £500) for next purchase