To cancel your booking and get a refund of your ticket price (depending on the fare conditions of your ticket), please contact the agent/office where you booked your ticket, or if you changed your booking, contact the office where you last modified it.
For bookings made (or changed) at qatarairways.com, you can request a cancellation or refund at https://www.qatarairways.com/en/refund-request.html
For assistance contact your local offices, contact details can be found in the following link https://www.qatarairways.com/en/worldwide-offices.html