I have always found the DATC tests to be a good reference when you're unsure of the results of a move:

https://webdiplomacy.net/datc.php

You have understood this wrong.
Your question is a bit unclear. Unit A being attacked has no impact on move/convoy orders given to unit A. But since you are asking about convoys specifically, I will answer that question. My advice is to either do bot games, or watch some youtube videos on the rules.

In short: a convoy order is always succesfull as long as Fleet A is not forced to retreat.

[quote=Bakaron post_id=247649 time=1626088037 user_id=19593]
If unit A is attacked by unit B, shouldn't any support hold/move/convoy orders given to unit A be cancelled?

I am in a game where a fleet was attacked and the convoy still went ahead as it they weren't targeted by an enemy unit.

Have I understood this wrong or is convoying broken?
[/quote]

A convoy is not disrupted/cancelled by an attack. A convoying is only disrupted/cancelled if a convoying unit (Unit A in your example) is forced to retreat.

If unit A is attacked by unit B, shouldn't any support hold/move/convoy orders given to unit A be cancelled?

I am in a game where a fleet was attacked and the convoy still went ahead as it they weren't targeted by an enemy unit.

Have I understood this wrong or is convoying broken?