Lastminute.com Extremely poor service & peculiar computer

I would not have believed I could have so much trouble booking a hotel room. But Lastminute.com cost me virtually the whole day to try and put right their mistake.
The problems started when I attempted to book a room for two adults to share with two separate beds. I told the Lastminute.com agent quite clearly what I wanted and he repeated it back to me and we concluded the transaction (or so I thought).
Shortly after, an email arrived but it said one adult and not two as I had asked for.
I called back and talked to another agent who said ‘don’t worry Lastminute.com will cover any difference’. But when I checked with the hotel they told me the second adult would be turned away and that only Lastminute.com could make any changes to the booking. Anything else would result in the loss of the money already spent. I was also told the booking had not showed up yet and maybe if I left it until the following day it would be OK (not quite sure how that works but I agreed to call back).
On the third contact with Lastminute.com the next morning, when I asked to amend the booking, I was told to ring back in about three or four hours because the computer was not working.
Just a few minutes later, on the fourth attempt, I said I wanted to make a new booking but first I needed to check my existing one. The agent managed to look up my booking but when I asked to change it apparently the computer had suddenly mysteriously gone down again. I was put through to customer complaints who spoke very quietly, would not speak up and kept telling me I must call back later in about 3 hours.
The last agent, five minutes later, was more helpful. Somehow, maybe by magic the computer was working again, she contacted the hotel, got them to amend the booking and said she would send a confirmation email. I checked with the hotel who confirmed the changes and that I must pay them extra when I arrive.
But I still have not received any confirmation email.
It is extremely unlikely I will use Lastminute.com again and will recommend any one I meet to avoid using it.