[helene_t]

The specific situation 1♦-(2♣) is akward because it does not belong to any of the obvious categories:
- After an opening in a major suit, the reopening double does not show extra's because we can always fall back on opener's 5-card.
- After a 1-level overcall, it does not show extra's.
- After a jump overcall, I think it does show extra's.

The situation 1♦-(2♣) is easier in a weak-1NT system because responder can usually compete with 8+ HCP's . Therefore, you can agree that the reopening double does show extra's. When playing a strong-NT system you can't do that (at least not at matchpoints) because responder may have as much as 9 HCP's.

I wouldn't have opened the south hand. Three-suited hands with a black singleton can cause rebid problems. Your initial pass is correct and I presume that opener's reopening double is correct too. Your second pass is questinable but not necesarily wrong. The LOTT tells you that 2♣ is likely to be enough. I think it was bad luck.