my laptop has been in for repairs for over a month

I returned my 4 & 1/5 month new HP laptop to HP shop, it was collected on 18th March, since it was collected I have called frequently to find out when it will be returned fixed, I was told that it had been repaired & would get it delivered yesterday, when I didn't receive it yesterday I called again & queried. To be told for the 2nd time that the incorrect part had been received? they told me this a week after it was sent in, so I can believe that an incorrect part could be sent once, but definitely not twice. I requested the job number so I could ask HP to follow-up & they said they will let me know. I'm not even sure where it is?