Sharraxaadda

We believe there is a large sinkhole that's formed in our front yard. Whenever walking over a particular area-the ground sinks under our weight. We have tried to top off the area with additional soil but the problem remains. This week we inserted the 5 foot handle of a garden tool into it and it easily penetrated the area without any resistance at all and never reached a "bottom". When cutting the grass, we fear a cave-in or worse. We have no idea who could help us with this. In the past, we have experienced other sinkholes on our property and the Dept. of Highways, we believe, realized that the storm drain running thru our property had developed breaches and caused these sinkholes. There is another street drain not far from our current situation. Could you please advise us ?