Copy of old tax returns for UK non resident

I need to obtain a copy of the tax returns I filed in the period I worked in the UK (tax years 2011 to 2014). I've lost them and need them for personal reason in my home country (Italy). I tried to register an account in the hmrc site but the national insurance number I provided has not been recognised nor my post code (either the one I used when I was in the uk ot the italian one). Can you suggest the best way to proceed? Thanks.

Hi Giacomo Gargano,

You can telephone +44 161 931 9070 to aks for copies.

Thank you.