Agreed fully that there is nothing that the OP or ISP can do about it, if it is aluminium.
I posted that data simply for comparison; and given his 33db attenuation, the basic rate is unlikely to increase by much.
My only experience of aluminium wiring is with a 1990's Alarm System, for the domestic internal wiring.
I have tried searching for the use of aluminium wire on the phone market; but so far I have not found anything relevant.
Do you know if and when aluminium wiring/cables was used for the Exchange to Cabinet and onward to Domestic premises, was prevalent?
I suspect that it may have been in the 1960s and 1970s, as back in the 1950s, the underground cables were copper, soldered joints and encased in sleeves with "wiped" soldering, traditionally using beaver skin. Quite an art on itself!
Thanks for any information you can provide on those aspects,, learning more every day.