Finally I received the 2 coupons I applied in April, I found a place where you can redeem the coupon and get the converter box for free. Here is the website address: www.egridlink.com.
They are selling $40 for one coupon box which equal the value of coupon government issues, there is a $2.99 handling fee plus shipping applied, but after I compared numerous retailers, they are still the lowest after handling and shipping. I already placed my order and hopefully to receive my converter in the next few days.