What is the situation if I get a gift worth about 53 euro by redeeming loyalty points. I would have to pay for postage. Would I have to pay duties even though the item cost me nothing?
There is a gift exemption up to a total value of €45 including all transportation costs. See here.
Yours isn't a gift though, and as it's valued above €22 and under €150 in total, you'll just be liable for VAT and potentially a service charge for administration. There's a chance your parcel may slip through unchecked, but I'd expect the charge.