My impressions are the reverse, Ana I've only ever had good experiences of Tesco Customer Service. My latest last week, when I emailed them to report a missing item in my online order (a very small one that I think I might have overlooked myself when unpacking the boxes). I just mentioned as an aside that most of the fruit was damp on arrival and it might be a storage issue. They refunded the lot, over £14, even though I said it was fine after a quick rub down with the tea towel!
But Asda I've had so many bad experiences. For starters my only online order was hours late - they didn't have satnav or a map and must have rung us eight times for directions as they circled round our address. And when I reviewed my experience, as requested, I didn't even get a reply, let alone an apology.