Incoming talk Sound and Volume is too low!

Just bought Iphone 5s 16 GB, but can hardly hear incoming talk and "other end" ringtone, have to really press the phone into my ear.. have no time for repair sending. Anyone out there has a sensible advice other than "pressing the volume buttons on the left" which have NOTHING to do with the volume on incoming sounds? Nor other mediocre replies such as cleaning the (new) phone with a toothbrush, or piercing something with a needle..

Thank you! I'd appreciate a good advice..!