Upload speed is not guaranteed, download speed is ,
if your guaranteed minimum download speed is 23Mb , and you are not achieving that , report it , your speed isn’t being monitored so you need to report it otherwise it’s not likely to return to above the minimum, if there is a problem your provider will seek to rectify that , and if that can’t be done you are due compensation and potentially offered a penalty free release from any remaining minimum term .
Looking at your postcode for speed is pointless, you were given a bespoke speed estimate when you joined , that is the standard that needs to be met.
Why are you not getting those speeds you ask , which speed though , it’s 23Mb not 28Mb guaranteed, so why are you getting less ? , there are many possible reasons , like a line defect, an internal wiring defect, other devices using some bandwidth at the same time as you testing speed , call and report it , those things can be looked at .
