Spice Jet Airlines — i upgraded my seat by paying extra amount for leg spacing but i was not given the seat for which i paid extra money

Address:

Bangalore, Karnataka, 560041

I was travelling from bangalore to bagodhra in spice jet the flight is at 12 noon.. I was asked to take a priority seats so that i would be given a extra leg space as my foot was injured a bit, so i paid extra money n purchased the seat as suggested by the staff, but once i boarded the flight i wasn't given the seat which was promised to be given for the extra money i paid
I spoke to the cabin crew they asked me to write back n email for requesting the refund
Kindly do the need.
As i have paid extra money for the seat but i haven't been given the seat.
Thanks
Regards
Chaitra