Our factory has stopped producing this product since long time ago.
We stopped manufacturing this product a long time ago
PS:stop是瞬间性动词,不能用于现在完成时或接表现在完成时的时间状语比如for..since...
我们厂早就不生产这种产品了。
Our factory has not produced this product for a long time.
It has gone out of production in our factory.
Our factory has not made this product for a long time.