Trying the test socket rules out internal wiring issues (extensions).
Different modems report different attenuations.
Different modems also sync at different rates.
Your neighbours modem may show a lower attenuation and sync higher on your line.
I synced around 44Mb (used to be 55Mb before crosstalk).
My neighbors either side of me both sync around 32Mb.
Your line can take a slightly different route to the cabinet than neighbours or be using lower quality cabling(different guage copper, older wiring, sections of aluminium) at some point on the run to the cabinet.
What goes against you is that the ISP's work on a range of estimates provided to them and they quote you a minimum guarantee.
Your sync will be above that so they will not want to send anyone out to try improve this.
If they did and no fault was found this visit would be chargeable to you at around £130.
What your neighbours get is irrelevant. Every line is different and there will always be some lines that just perform worse than others.
That's why they give a range of estimates.
You can check your lines estimates by entering your telephone number or full address in to this site.
https://www.dslchecker.bt.com/Trying the test socket is your best option at present.
If there's an improvement in sync speed then there may be something you can do at your end to improve things.