I don't know about minimum spends but the offer was 20% cashback up to ₹250 on the first bill paid in the month for utilities (Gas / Electricity / Telecom / DTH). "The offer will be valid for transaction made from mobile app and web portal of the respective utility vendors." Details here:
https://www.saraswatbank.com/content.aspx?id=Utilitybilloffers Now reduced to ₹100 from 1st April after ₹250 for many years
🙁 So I used to do for bills of ₹1250 value or a little more. Even if bill is 1500, you will only get ₹250 (now ₹100) cashback.