I felt morally OK with the situation...
Only, my contract did have a noncompete. But then, this is Sweden, and noncompete clauses are almost not enforceable by Swedish law. An employer can't stop an employee to take another position. To be a valid clause, an employer must offer the same payment the new position would have had whilst riding out the non-work period, and no one does that.
A strongly worded letter from my lawyer sorted it. Never heard from them again.