Simpl Pay later - Payment already done still harassing for payment

On Oct *nd I made a payment for INR ****.** which was for the services usage frm **th Sep to **th Sep. After I made payment the dues were showing as INR *. Them after using the services frm *st Oct to **th Oct, I got another bill of INR ****.** which I made a payment for on **th Oct. This time after making the payment was still showing as dues pending and it didn't reset to INR *. Same time various technical issues began after which I wasn't able to use Simpl pay later in other vendor apps like Big Basket or Myntra. I immediately realised there is a technical issue in the back end of the app and it's causing issues. I have getting calls regularly on which I have explained that my dues are paid off still system glitch is there but nobody is ready to listen. Now I am getting legal action threats for payment..I have made huge payments like INR **k for my usage so paying INR ****.** is not the issue, the issue is Simpl accepting their technical glitch and harrassing me for payments.