Customer service promise?

Hi, looking for a little advice...
I have had my mobile handset for under a year and there was an issue with the battery, it was sent in for a warranty repair in November to Knowhow (Carphone Warehouse repair service). It was returned after 10 days as 'repaired', however the note said they had 'cleaned the charger port'. (Charging was never the issue). As predicted the battery issue was the same and I was left with 2 options- send again for a repeat repair (not much faith after round one) or concert the manufacturer, which is Google. I did the later.

Google performed their troubleshooting remotely and have told me the handset should be replaced and offered to do so but it would take up to 2 weeks. I need my phone, gps, emails etc for work and couldnt send it off again any time soon so was advised to contact the seller for a faster option. I did so and was offered a speedy store replacement and because of the hassle offered the newer model. I was also told I could go in that evening to swap. (great!), I called the next day to check they had stock and was once again told the quickest option would be to get the phone checked in store and they could provide a replacement on the spot.


However, I went into store and was told I had to go through CPWH 'repair' process once again and not guaranteed a new phone, and the person who told me I was due to be given the newer model had misinformed me.

Where do I stand when promised a solution? I understand this was generous of them but I am also not in a position that I can do without my phone again for 10 days, possibly only to be told it is fine and to be cleaned. I have made a complaint but have been told this is for internal purposes and not not impact the procedure of the repairs process.

thanks