Lost sim card

[mangle]

How do I go about getting a replacement?

This is for orange btw

[Robbie]

Call Orange on 07973 100 450

Just explain and ask for a replacement, I did and got one 2 days later

[Sunny.]

Same happened to me except my got stolen,

Rang them they asked for the 4 digit ID code and simply blocked the sim, and sent me new one.
Should be getting it monday/tuesday

[Muggseh]

Yer same, They send you a replacement sim card all you need to do is just register it as soon as it comes through the post.