You guys are fraud! They have not delivered the ordered items and don’t have even a solid reason to them. As it seems to me you did this cheap marketing thing only for making the maximum Apps Install.
Fault is yours, you have to be prepared or make that type of condition for purchasing that after single or 2nd purchase that free coupon will be expired. If there is any such type of terms and condition, you should mention before hand not after placing orders and confirmation.