Reliance Jio Infocomm — Reliance Communications Refund of security deposit of jio fiber account

I have a jio fiber connection with number [[protected]] my mobile number is [[protected]],
I had my jio connection on Feb11th & had done advanced payment for 3 months

Cancelled my connection on May 8th & setup box was picked up on 11th.

I havn't got my refund yet, called customer care they are saying I have an overdue amount but when everything was paid in advance & was cancelled on time then why there is a overdue

case number : SR00001C8JCY which is open from 4 months