You're getting something that's key to your problem wrong. Order of operations. From the rule book:

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2– Xenos move 1 Zone toward their destination Zone by

taking the shortest AVAILABLE path. IMPORTANT: Closed

doors are not taken into account to determine that path.

If a closed door bars the path to the next Zone toward

their destination, all Xenos in the Zone spend their Action

destroying it instead of moving. Flip the door token on its

destroyed side. The way is now open. A destroyed door

cannot be closed again. Mold application (P. 20) removes

destroyed door tokens.

"Xenos move 1 Zone toward their destination Zone by taking the shortest AVAILABLE path." (Moths would move three zones instead of one.)

• An available path in Zombicide, all editions, is a path that is not blocked by obstacles.
  
• First, they determine their path. If there is an open path, one that can be used to reach a survivor. Plot the course.
  
• If the path is blocked by a door or destroyable barricade they move up to the door. If the Xeno has MULTIPLE ACTIONS [Not multiple moves.] the first action is used to move up to the door, the second action is used to destroy the door.
• If they only have ONE action, like your moths, they move up to the door and stop. On the next turn, they break down the door.

Here's the part I think you're getting stuck on.

IMPORTANT: Closed doors are not taken into account to determine that path. If a closed door bars the path to the next Zone toward their destination, all Xenos in the Zone spend their Action destroying it instead of moving.

• Doors are not taken into account when first determining that available path. This means, if there is a closed door along the way that would lead to a shorter path, do not consider it as a viable pathway. That path is effectively a wall. Keep the Xenos moving along the unobstructed path that leads to survivors, ignoring all closed doors.
• If the door blocks the shortest path, meaning, there's absolutely, positively no other way around, for example a single hallway with doors at either end and the survivors are on the other side of the door. There isn't a T-junction that the zombies can use to go around to reach the survivors.- THEN that's when you use the door opening rules above.

It goes like this - Xenos look for survivors. They find that there's two of them. One is 4 spaces away, but is behind a door in a room that cannot be reached without going through the door. The other is 8 spaces away, the Xenos would need to turn left at the door, then right at the next hallway to reach that survivor. However, the pathway is completely open already.

They're going to go towards the survivor that is 8 spaces away and ignore the survivor behind the door. Doors break line of sight, require an extra action to open and can be opened by survivors, unless destroyed.

Now, let's say the Xenos move one space passed the door, it's one space behind them now, trying to reach the survivor down the corridor who is now 3 spaces away.

The survivor in the room opens the door but doesn't move. The pathway is now open. On the next activation, the Xenos are going to turn around and go back towards the door with the survivor that's only two spaces away because the path was opened when it was time for them to plot their moves and that survivor is closest. [We're ignoring noise in this example.]

Doors are only destroyed when there is no other viable path to survivors and the door blocks the path.