So curve ball... it looks like it's the ONT itself.. openreach engineer hardwired directly from ONT using cat5e and cat6 to his laptop.. only pulls 150mb.. he rang his techs.. who said there is 988mb coming into the property upto the ONT.. but it won't spit out anything over 150mb.. after an hour of trying different cables and many speed test sites.. he had to walk away at a loss, and sat it's on BT.. because there's 988mb upto the ONT anything past that point is not their responsibility... so no clue now, paying for 900mb and getting 150mb.
Sounds as though the ONT itself is faulty. I would have expected him to replace it. I suggest you push for it to be replaced.
unless it has changed the 1.6gb connection with EE was only for new customers not switches - at least not yet