The problem with "returning" the phone under WARRANTY is that the store will send it to a repair center authorized from Nokia, which is in fact some "corner repair shop" that made a deal with nokia.
Here in PORTUGAL the repair shop (TAMET) is well know for it's BAD SERVICE. There are some amazing public complaints against them.
My previous NOKIA 5 was sent to them, after 2 MONTHS of problems (tried every debug and reset on the book... and waited for a fix from nokia, but realized this was more serious than that, probably a hardware problem). THE REPAIR SHOP said "This phone has NO PROBLEM"!
Now... it's my PROOFS and word against someone i don't know, that made tests i don't know (if it even made them!!!!! they are well known for returning the phones untouched just to comply with deadlines).
SO... this is a tricky problem!!! 1 MONTH without phone and several complaints, still no END to this!