Inventory Biz — unprofessional service, terribly poor support & no bill

I have purchased inventory biz single user (Gst), barcode printer, scanner bullet, thermal printer from their kochi dealer around 3 weeks before. Installation it'self was delayed few days, the sales executive was keep on dragging the installation.
I made the full payment on the day of installation and started waiting for the bill. Nowadays, dally i am making calls to that executive and he is not giving me the bill.
Terribly poor support from their helpline numbers, the numbers are always busy and till now i am not able to talk to the customer care...! Today i made a call to their head office number (Provided in the website http://www.inventorybiz.com/) and tried to convey the complaint but he said he is dealing with sales only...! I don't know to whom i need to escalate this issue. This is my final attempt next i am planning to move legally against them.