LED lamps keep glowing when dimmer is turned off
Buy a dimmer designed for LEDs. Your typical light dimmer puts out pulses of power; the brighter the setting the wider the pulses. This is OK for incandescent lamps as they draw lot of current and need a brief time to turn on and off.

LED lamps draw about 1/10th as much current and turn on and off in millionths of a second, so the same narrow pulses that make an incandescent light dim will make an LED light at least medium bright, maybe even flicker a bit.

You could "cheat" a bit by plugging in a incandescent bulb off in a corner to act as a minimum load which helps the LEDs behave better, but in the long run it is best to install the correct dimmer for the LEDs. Almost any hardware store should have them.