Air Arabia — Extra cash charged other than flight charges which is not in the ticket

I have booked a ticket with pnr no[protected] from Thiruvananthapuram to Sharjah.
My actual date of travel was 1-05-22 due to some reasons i want to change my date of travel with the flexi fare option of 1 modification available in my ticket 8 hours prior to departure.
I called the air Arabia customer care number [protected] and asked about the same. He told me that i need to pay only the fair change applicable that is 3000 something Indian rupees.
The Next day I called the same number and asked them to send me the payment link. They sent me a payment link of 8020 Indian rupees. I didn't make the payment and I called again for confirmation. Then they told me that it's only the price difference and there are no extra service charges or anything included.
He sent me the link again then I made the payment.but when i received the Ticket it is clear that the Extra charges are only 3902 Indian rupees.