Southwark Council: you can report issues such as graffiti, fly tipping, dog fouling or potholes to Southwark Council via Fix My Street. It allows you to see if the problem has already been reported and to receive updates; you can attach photos too.
Southwark Council also offer a free graffiti removal service for private businesses, see their website here. 

Lambeth Council: you can report graffiti or fly tipping to Lambeth Council online here

Obstructions on pavements: report to Southwark here and Lambeth here

Private Roads: contact the Dulwich Estate on 020 8299 1000 or via their website here

Water leaks: contact Thames Water via their website here.

Badly parked e-bikes: report via Fix My Street or direct: Human Forest, Lime Bikes, Bolt Bikes, Dott

Network Rail property: call 0345 711 4141 or report it to Network Rail online

Telephone boxes: call BT on 0800 023 2023

Bus stops or bus shelters: call TfL on 0343 222 1234 or report it to Transport for London online

Virgin Media cabinets: report it on their website here or call 0330 333 0444

Openreach cabinets: report it on their website here

Post boxes: call Royal Mail on 03457 740 740