Still waiting on parts- Samsung Galaxy S4

Hi I previously posted a compliment on the friendliness and efficient service I received in store. Issue now is I was quoted 2-4 working days on a fix, I handed my phone in on the 23rd of April, it is now the 6th of May, 7 working days later, I have been told they are awaiting a main board and they cannot give me an ETA on when the part will arrive, If you sell the product surely their should be parts readily available... I am being highly inconvenienced and would like this matter resolved urgently and an ETA as to when I can expect to have my phone back. My service order number is ***