No feedback from repair centre, lapsed turnaround times

I had been having issues with my device (still under warranty). I had Samsung check it, who had wiped the phone and reinstalled the software but the problem remained. I then took it in to Vodaworld, I got my device back very quickly where they'd said they found no fault. The very same day the screen had started showing worse errors than before. I then returned the phone to Vodaworld. I received an sms on Monday 28 July that spares have been received. I have had absolutely no follow up updates since then. I have had contact with a person at Vodaworld who would try escalating the problem but he too has not been able to get any response from the repair centre. Surely if they are unable to fix it, it should be replaced as it is still under warranty instead of going no-contact. The 3-7 days turnaround has lapsed.