Roomster Rear door lock

Hi there, need advice/help on the following issue on a Roomster 1.4tdi 2007, rear door lock.

The original problem:

Rear passenger door would not open from either handle. the actuator wasn’t making a squinty noise when unlocking off the key fob/ internal central locking.

With the door locked managed to get enough of the door card off to force the lock open.

The solution (i thought anyway)

Replace the actuator however , every actuator i’ve bought once fitted would not open the door from either handle, but only after the central locking had been engaged. After a lot of wiggling and pulling the on the latches i managed to get the door open to remove the actuator

i’m on the 3rd actuator, which is a brand new main dealer part. Same problem, once fitted you can open and close door but when you central lock it you can’t open the door from either handle. eventually after banging the outside of the door the door half opened and then i used a small angled tool to release the latch. i don’t believe all 3 actuators are faulty especially as the current one is brand new. (the previous second hand ones would not even half release by banging the outside of the door like the new one has. I removed the new actuator, and manually simulated the closing of door. i can open it even after i central lock it (remember it is not mounted onto the door). Does anyone have any experience or advice they can offer? thank you