Chamberlain garage door malfunction from the start when it was install. works for a little while and then stops. Internet, Arazona

I purchased a Chamberlain garage door product. It has not worked right since I got it. The door will go up but putting it down does not work. I have to get out the car and hold the wall unit button down and even then there are times the door will not go fully down before returning to go up. I have complained sevral times and I cannot keep paying people to come out and fix something that is never fixed. I tried to send them a report asking them to replace their unworking product but the page only gives me an error message and will not let me send the report to them.