Why would the neutral current be significantly greater than phase current?
On a single-phase, Euro-style connection, neutral and line must be equal - if they were not, your RCD would trip, because looking for unequal line and neutral is how it detects ground faults.
If neutral is larger than line, then my only guess is one or more of your neighbors has a broken neutral wire, and their neutral is returning via their neutral-earth bond, their earthing rods, the earth, to your earthing rod via your N-E bond, to your neutral.  We see that in the US from time to time.
Check with the power company, and make sure you’re not paying for that.  If they bill you for Line current only, that’s fine, but if their bill is based on the average of L and N, then you’re buying your neighbors’ power.