There is nothing like bad luck, however I think you have a few options here.
1; spend £1000 + at the Alfa agents.
2; Try All Car Electronics in Derby/Staffs, they may be able to decode the ECU if the unit is one that can be done. About £150.
3; Alfasport in Cambs maybe the last resort, but it is a fair way to travel, but it would end up far less than what the dealers would charge.
4; Second hand, I did buy a keyless Alfa once...big mistake, got a s/h key set off a GTV running car, installed it and hey presto, key code light stays on. So then started to go through all the hassle and expensive or trying to get it going, but in the ended got hold of another key set and if it worked I paid for it, if it did not work no pay!! Luck was on my side and it worked.
I can really relate to your problem as well, because we also got the entire set including 3 keys and the brown, and this made no difference if you do not have the original key code number supplied with the car from new, and then it is only luck that that will be of any use.
Hope you have good luck with the 155.