Indigo Airlines — while changing booking date the booking cancelled

PNR .T95SQJ.i had booked on indigo 30 apr kochi bom.since i wanted to change i Went to indigo site manage booking .while trying to change to my surprice i got message my booking is cancelled and a refund balance of 1100 will be debited to my debit card after deducting 1500 xlation charges.what thw hwll is hapening with indigo.this is cheating wen i did not press the cancellation.i Had to bOok another ticket paying 5000 .this is day light robbery by indigo.