Collapsing pavement and sinkhole

The pavement in front of our house has started to sag and dip, and a sinkhole has started to form in the tarmac by our gate. The drains in the road were flooding lots at christmas and I reported them (you sent the gully sucker out in january). However since then the pavement has sagged and a sinkhole has appeared. I visited the council archives to try and figure out if any services pass under this section, and the road drains drain to a soakaway under our driveway apparently. My understanding is that despite the soakaway being within our land, its the council's responsibility to maintain it. I am now concerned that the soakaway isn't functioning properly, or the soakaway pipe may be blocked and this is having a knock-on effect for the stability of the surrounding area. The tarmac at the join for the pavement to our boundary wall is starting to crack too and I don't want there to be any issues with our driveway access or indeed the foundations of our home or stability of the wall, as the soakaway is from the 1960's and is located less than 5m from our house which isn't acceptable by modern standards. Please could someone investigate?