Vodafone upgrade mess

So I upgraded about a week ago as my upgrade date was 1st August and the plan ended 15th October. The first upgrade advisor said I had to pay an upgrade fee of £210 because ;

At the moment the only way you can decrease a price plan is at the point of upgrade, you aren't currently due an upgrade to 06/04/2016 so if you wanted to upgrade today there would be an upgrade fee involved

I didn't necessarily mind as I thought I must have got my dates mixed up and new my current phone would have paid that off.
The advisor discounted this down to £168.67 so I wasn't too annoyed with that.

The more I thought about it though, I felt I shouldn't have paid anything so I got back on to the chat and was told ;

What if I can try and waive the amount for you today?
Vinay: Would you consider keeping the contract if I can waive off the £125 plus the £43.67?

Obviously I thought that was quite a nice offer so I agreed to continue ( I had already paid £43.67 as they told me the bill couldn't have a charge higher than £125 added at one time?)

So, the upgrade arrives and all seems to be well....... until my bill arrives!
£138.94 charge! No idea where this figure comes from as it doesn't add up to what the chat advisors had even said.

Going onto the chat I have been told I have to pay this ; trying to return the device is a nightmare as I keep getting passed from pillar to post. Then other advisors are just simply saying

if you have been promised something you will get it for sure.

All well and good saying that but not when a bill of nearly £200 is on the line