I really hope someone can help.

I have an Audi A3 TDI 61 Reg plate and it’s been broken into THREE times in as many years while parked right outside my front door. I keep the car locked at all times (I swear!) and somehow thieves are still getting in. I’m getting mixed messages on this from various garages and technical specialists. No one seems to give me a straight answer.
 

firstly, I want to know how on earth they’re getting in and what do I need to do to guard against this happening again?!

I knew the previous owner - she was a friend of my parents so I don’t believe she ever had the keys cloned as she would have told us.

Worth noting that my car is the only one on my street that this is happening to. 

It’s not a keyless entry car. 
 

Secondly, the thieves stole a Sony AXV 3500 stereo/bluetooth hands free kit that I had fitted 18 months ago. The car alarm has also been disabled. A garage couldn’t get the alarm to come back on, even with a diagnostics kit, but it was definitely working before the theft as I accidentally set it off a few weeks before hand. Some people have said that the alarm has stopped working because of the missing stereo unit and that putting in a new one will get it working again as it’s all connected. Others have said this is nonsense and they’re in no way related and that the alarm repair is a separate issue. I’m getting complete mixed messages and I’m so confused. 
 

Can anyone help please? 
Thank you!

Gemma.

Am I right in assuming there is no sign of damage to the doors etc? If so, your car has not been broken into; it has been entered by the normal method of simply opening an unlocked door.

Two possibilities occur to me:

[1] Somebody else has a key to it. Do you still have the spare key that came with the car originally? Could the previous owner have had a duplicate key made as a result of losing the spare which has found its way into another persons hands?

[2] One of the doors or the boot is not locking when set. Have you checked that they all lock when you turn the key? It is not unknown for the lock mechanism to fail on one door while the others work normally. That can be caused by a broken wire or a faulty lock.

I can imagine that the alarm was fed by the same electrical supply as the Sony and maybe that is the cause of the problem, but that is entirely a guess on my part.