Starter runs without stop even when ignition is turned off

[deedoo65]

I have replaced the battery for my T reg laguna recently. Everything ran smooth for a week until I had a problem with the starter. When I switch the engine on the starter does not stop even after I turn off the ignition and remove the keys.

I tried to disconnect the ECU unit and reconnect it. I also unpluged and repluged the black relays near the battery the trick worked and I did not have any problem, until two days later when the immobiliser went on by itself and I could not put it off by the remote.
I had to disconnect the battery to silence it. I went to read some forums from here and decided to wait before I attempt to reconnect the battery.

Any suggestions of what is going on are much appreciated.