Ah that will be your problem. If you are 2.5 to 3 miles away from the cabinet I am surprised you are getting anything at all. See graph for speed over distance
You won't get anything like that speed if you are that far from the cabinet.
You should contact BT and request and engineer but there will be nothing he/she can do if you are on the far away cabinet.
All he/she will be able to do is confirm which cabinet you are on and that you will not get your minimum guaranteed speed. This will allow you to leave your contract with out penalty should you wish to do that.
That's my fear, but why would they switch me to a different cabinet that is slower than the ADSL?
Cabinet 9 is newly built and I had assumed that it's construction enabled Cabinet 5 to be connected to the exchange aswell
I have no idea why you were switched or what the intention of Openreach is with regards to the cabinets.
As I have said, you will need to contact BT.
You have an enormously long line for Fibre. The BTw Checker & BTr promises are lies.