Super SLOW Faster Fibre speed

Hello,

I have been getting constantly slow speeds of around 4-5 mb/s. I have been in contact with customer support but no reply. I cant even stream Netflix with Fast Fibre broadband. I am connected by hard wire to the router which is connected to the new BT dual socket box.\

Could you please tell me why the speed is so slow as I can get those speeds with just normal broadband.

 Thanks.