How do I get water flowing back into the cistern ???!!!???

I do have a dual flush caroma flush system. There appears to be a blockage which is preventing the water from flowing into the cistern. There is some sort of plastic device which goes up the cistern nozzle and the end of which sits in the connector, which fits to the cistern. I have checked and flushed the connector, and there is definitely water flowing from the tap to the cistern. It just isn't flowing into the cistern. Can someone please fill me in as to how I can rectify this problem???!!!???