You'll get points on vouchers & not on entire transaction. In your case, you'll get rewards on each 2000 vouchers separately.
I learned one thing that we'll get rewards in multiplication of 200 that means voucher of Rs. 250 will get 12 rewards (magnus). We'll not get reward for extra 50 rupees.
If we buy 4 vouchers of Rs. 250 then rewards points will be as mentioned below;
1. Rs. 250 - 12 RP (1x)
2. Rs. 250 - 12 RP (1x)
3. Rs. 250 - 12 RP (1x)
4. Rs. 250 - 12 RP (1x)
So total 48 RP (1x) for transaction of Rs. 1000