Idea Cellular — Amount INR 150 charged for upgrading sim from 3g to 4g in VI retail store hyderabad

HI, I have upgrade idea sim from 3g to 4g in vi care retail store in Hyderabad and they have charged me INR 150 for just upgrading the SIM. when I reached Vi care support team over twitter, they informed me it was not right way to take money from customer and its free of cost for SIM upgradation. On the token of inconvenience caused to me they promised to provide a coupon of INR 100 and assured me that these kinds of issues will not be repeated in future instances. After couple of days, I have waited for the coupon/reward from them, but they literally ignored my request and not response from them. Thought this forum is bit help full and raising complaint here. Help me to get the issue resolved.

Thanks,
Saikumar