Got the key today but it wont open the door

I had a look at the original key lying in the boot/trunk and the grooves
are worn down a hell of a lot compared to the new key.
Absolutely p*ssed off now with this now, I called BMW and they said it looks
like the only way is to retrieve the original key is by "Smashing a window"
I will need to source a window from a scrap yard first before I smash one
as the weather in Scotland is dire at times, in hindsight should have smashed
a window rather than buying a new key now it will be twice the cost.