How thick was the mulch placed on top of the landscape fabric?
What kind of "weeds" do you have? If they are invasives they will need to be dug out, but it they are the more wimpy types they can be covered.
Since landscape fabrics have numerous spaces between the threads that make up that fabric that will allow light to pass through and will encourage the seeds in the soil to germinate and grow, right through the fabric, unless the mulch is plunked down thick enough to prevent that. Usually that means the mulch needs to be at least 4 inches thick and often 6 inches which means that the landscape fabric is unnecessary altogether. However, "weed" seeds can accumulate in your mulch, germinate there and grow, and sometimes people think they are growing right through the mulch when they are simply growing in the mulch.