Southwark Noise Control. And record each call you make, as they won't necessarily do that. Or, find out their landlord/housing association/whatever and try complaining via that route. Or, get other neighbours together and put in a joint complaint. The problem I had with extremely noisy neighbours was completely resolved after months and months of frustration, but maybe there were different issues. Several lots of neighbours got together and complained to the Housing Association. Not easy as we got fobbed off and passed around different departments, but it worked in the end. Good luck.