Shiprocket — Overcharged even after giving proofs

Hi, so last year I used Shiprocket to ship certain items. Initially they were good but after that they started overcharging me. And deducted money from my wallet without prior intimidation. After that they put my balance in -
Now they're threatening me.
I don't understanding i already paid the shipping amount of each and every parcel. Now why are they asking extra money. Please help.