Univa 3-plate stove : knobs and the oven are not working

I am not happy with the Univa 3-plate stove I purchased at your store in March 2025. The knobs and the oven are not working. I enquired at the store last month, and they promised to send a technician, but I have not received any attendance. I do not understand why this has happened, as it has not been long since I bought the stove and I am still paying.