Spice Jet Airlines — complaining about baggage charges

I booked a trip from male to blr. Via trivandrum in spicejet. The pnr is n45ytl.
Name : soumesh bhattacharya.
Now as i was traveling from mle i have a check in baggage of around 23 kgs n hand baggage of 9 kgs.in trv they charged me 8kgs extra that too 500per kg.
As i was traveling from mle to blr. With the bloody same airlines. They should be flexible enough. Another thing is if you say that it's rules of domestic airlines then how come it's 500 instead of 300. This is actually a kind of cheating to the customers.
And this would be my last travel with spicejet in any trip.