Airliner 99 pilot reported severe icing conditions resulting in flight cancellation.

Narrative

Plane was in the hangar overnight after the ice storm impacting ZZZ; and was clean without ice when cargo was loaded. When cargo was finished loading and I called for release; we noted that the ATIS was now showing moderate freezing rain and thus according to GOM was not allowed to dispatch. After a 1:30-2 hour long delay the ATIS showed moderate rain; however the outside air temp was -1; but we reached a decision to attempt de-ice of the plane and launch; if I was comfortable with conditions on the taxiway and runway. The ramp was covered with about 1-2 inches of solid ice; with slush and snow present. Aircraft X was towed out into the alleyway between planes; and deice was started. The deice fluid melted through thin portions of ice before sliding in between the ice layer and the ramp surface; causing an extremely slick surface on top of ice that could move on top of the ramp ground. I was in the process of doing a surface contamination check on the left horizontal tail surface when the crosswind picked up; however I was not looking at the plane and only felt myself getting knocked down into the ice from the tail. No injuries were felt; the plane slid around 85-90 degrees into the wind. The plane only had one pair of chocks on the left main at that time. I called off deice and concurred with Dispatch that operations were cancelled for the remainder of the day.When I got knocked into the ground by the plane. Bad icing weather; an attempt to push for departure even with unsafe ramp conditions; and indecisiveness on whether or not all flights should be cancelled. Plane also only had one pair of chocks for deice in windy conditions.Immediately rechocked the plane when it was safe to do so; and told the deice truck to leave the area and told Dispatch it was not safe on the ramp with current winds.There should be a defined condition where all operations on ramp cease. Operations and Dispatch agreed that weather was bad enough that some planes would be grounded and flights cancelled; but other planes loaded and attempt to launch. Ramp was also slick; with heavy ice accumulation; and consideration should be given to using the hangar for cargo load in order to prevent further ice buildup on plane.