Power line adapter throttled since joining Vodafone broadban

[NICKC90]

Hi folks

I recently joined Vodafone broadband. It has been relatively plain sailing other than my power line adapter (TPlink AV600) to my office desk dropping to around 8Mbps, where with Now Broadband (previous ISP) I was getting close to max possible speed of 55-60Mbps. 
I have spoken with a Vodafone adviser via chat and they’re not interested, telling me it’s probably just a hardware issue. It’s very frustrating as it’s clearly the new router/provider. 
I’ve tried a few things, including testing the router direct to my laptop via Ethernet, which sees best possible speeds. But that’s not possible from the router to my office desk across two floors. 
Any help would be greatly received!

[VFbroadbanduser]

One thing that can throttle TP-Link powerline adapters is if you are using a high speed charger for smartphones or tablets plugged in the same room.

Basically they interfere with the powerline signal and degrade the speed. Older TP-Link powerline adapters have this problem because they can't filter out the signal.

[Cynric]

@VFbroadbanduser  They're also a bit unhappy if you plug them into a multi-way extension. They really prefer to be plugged directly into the wall socket.