I've done the following:
Reset network settings,
Soft reset,
Hard reset (factory data),
Vodafone have tested the network at Directors Office Level,
Vodafone have sent engineers to site (I met them there),
Samsung have sent WeFit to "fix" my devices (I have two of these pieces of *****),
Interestingly, We Fit engineer told me that they have told Samsung about this issue frequently but until it reaches a certain number combined with returns, Samsung won't touch it.
Samsung's response to me? Put the device in airplane mode for 15 seconds.
Couldn't make this ***** up, really couldn't.