Blockage and crack in surface water drain running from the manhole - just before it drops into the main surface water sewer

Hi We have used a drainage company to clear all our drains and do cctv survey There is a problem at the final point after the last manhole with roots and cracking which is holding up water. Our building has had overflowing gutters splillin onto the pavement below as a result. The Manhole takes surface water from shared various occupiers and has another shared pipe that comes into it before where the blockage is. Thames Water have said this is a Council responsibility and not theirs. Please can you help? I am happy to directly discuss or meet on site. many thanks