if you have a HH5 can you go to hub manager then trobleshooting then helpdesk and post 1-12
can you run btspeedtester and when first test completes then run diagnostic test and post results must be done with wired connection btspeedtester
can you enter your phone number and post results remember to delete number wholesale FTTC check
try quiet line test dial 17070 option 2 should be quiet and best with corded phone
BT Infinity customers speeds are not all the same. Your speed is affected by the distance you are from the Fibre Cabinet and the quality of your line, all of which can be different to other users so it is difficult to compare them.
If you carry out the tests a imjolly has suggested this will give the results that are individual to your line and will assist in seeing if there is anything wrong or if your line is performing as it should.