Withholding Customer Money as Credits

We purchased a specs from Lenskart. Due to technical fault(lens kept falling off) took it back and kept it with them for a month. After returning back I wore it but had some headaches. Also I found that the same fault kept taking place so we gave it back for fixing and also inquired weather the Lens was Wide focus lens. Turned out it was not which we were promised and payed for a sum of Rs. 14,000. They kept it with them for 6 months and on asking again and again they kept repeating that they are fixing it for first few months. In last 2 months they said that they have lost it. On approaching the store the store people abused us and asked us to get out of the store or face dire consequences. Finally on getting it back after another week, they were still not able to fix the issue. On being dissatisfied with the product and because no one can go without wearing a specs for 6 months we got it made form somewhere else. We wanted a complete refund for the product but the Lenskart people are just fixed upon giving us store credits so that we can purchase anything in future. We might not need another spec for god knows how many years. Keeping thousands of our money stuck is not what any customer would want. We want a full refund for the product following our dissatisfaction and the harassment we faced at the store staff. Please guide us the process and how much compensation we can get in the proceedings.