I-ON (Internet cable ) — Wifi Router purchased but Bill is not given by company

On 26th Jun 2014, I purchased wifi router from I-ON company for Rs. 1500/-, who is providing Internet services through cable in our area, is not providing Bill for same purchase. Requested them, but executives of company informed that we never provide the bills for same kind of purchase. Since Company is mention for 3 years warranty period for this router . We need a Bill to secure the warranty period. Need your intervention for the compliant .