We contacted al-ko for the same reason, the previous owner had not de-registered. I believe al-ko try to contact the previous owner to confirm that they no longer own the lock/van and then transfer ownership to you (a small fee is charged for this, can't remember how much though). The contact details are easy to find on their website.
You should contact CRiS too (if you haven't already), they will do the same as al-ko (also for a small fee).
Some insurance companies demand that the wheel lock and CRiS registration is up to date.
Hope this helps.
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