Comwave call centre offers a long distance services on November 24, 2011 with free minutes. Their website mentioned a different rate. Hence I did not use their free call. Their call centre continued pestering me to use the free call but I refused saying that I need their offer in writing before using it..
On November 29, 2011 I received an invoice dated November 24, 2011 (incidentally that's the day I received first call centre call from Comwave! ) threatening to forward to collection agency as "your account is severely PAST OVERDUE"!
Comwave is a scam. DO NOT TAKE ANY CALL CENTRE CALL FROM COMWAVE. Otherwise you are likely to receive threatening invoice to take your money. BEWARE OF COMWAVE!