How can I fix a problem with the water dispenser in my Samsung FF RS2iDCNS ?

We are having problems with the ice cold water dispenser. We have had the FF for 4years now without any problem. The water appears to freeze in the pipe so that it does not dispense water. The first time it happened, we switched off the machine, removed all the food from the freezer section, lowered the temp. down to -17'C, left the machine switched off for 24 hours. This cured the problem, unfortunately, after 24 hours the water had frozen in the pipe again. We went through the same procedure again, this time lowering the temp. to 16'C. Again this worked, but after 24 hours the same thing happened. We repeated the procedure reducing the temp. to 15'C but the same thing happened. I am aware that the recommended temp. is 14'C and do not want to go any further.
Can anyone out there help me ??