In short
Giant checked the bike and quoted to replace wires and controller for £350 as the connectors were corroded
After a few days, they suggested a new motor for £1k+ as replacing the wires may not solve the problem
I've said to them that the motor and wires were done by them under warranty...
The bike shut down unexpectedly. People at Giant are saying they can change wires for £400 but they are not too sure if that will resolve the problem as it could be a faulty motor too
Looks like they are just guessing.