HTC Wildfire - cannot answer calls

I have had my HTC Wildfire for a couple of months now and it has already been to the service centre twice and I am arranging for it to go back again. I cannot answer incoming calls (you need to drag the screen down to answer) so this means I have to call everyone back. It came back to me last week from its second visit to the service centre and is worse than ever. The screen freezes constantly and I cannot answer calls, send texts, look up contacts or basically anything I purchased the phone for. What a load of rubbish this phone is