AO Smith — unsatisfactory performance of ao smith water filter

The said product was purchase on[protected] and during the span of one year i was made to change one filter an now on 11.11.2017 the knob of tap got loose. The cost of knob is about rs.50.00only but additional visiting charges amounting to rs.400.00 were demanded which i didn't agree and the request was made to review the same but no action has been taken till date. My main contention is that at he time of purchased i was assured that the product will give uninterrupted service for at-least 3to 4 years. But within one year it has started giving trouble for one reason or the other. The company appears to me has cheated and given the defective peace. Please look into the matter for necessary action please