I never order G.fast because I asking BTw to double check the estimate on G.fast because I don't believe my line is 114-207 for download and 9-29 for upload. Should be 324-330 and 31-50.
Whether BT's database says 114-207 or 324-330, makes no difference to the actual speed you will achieve if you buy the service. That will depend on the physics of the line; the modems auto-negotiate to the best speed achievable.
If you *genuinely* believe that you know best, and you think the line is capable of 324-330, then simply order it and enjoy the speed. You can't complain for them giving you a faster speed than they promised!
If when it is delivered you get a speed between 114 and 207: then you were wrong and BTe were right. You can't complain for them giving you correct information!
Either way, you have no right to complain.