Clay Telecom services, India
Balance amount not return

I have visited Germany in April for that I have taken two post paid SIMs from Clay Telecom by keeping Rs. 5000/- advance cheque & 5000/- by blocking Cr. card, after returning on 21st April I sent the SIMs to clay for billing (as per their instruction) they sent me Bills for Rs. 3616 accordingly I instructed them to take payment from my advance cheque & return balance amount by cheque, also unblock my cr card. But till date I have not received the balance cheque however they have written me to send the cheque within four working day on 30th June.