Any one had much luck haggling contract renewal with three?

[Kanifee]

So my contract is due early upgrade with three and i have been looking at the Xperia z2 after using exclusively Samsung devices since the Note1, I have 2 contracts with them, mine and the better half's that also is up in 3 months.

I'm planning on giving them a ring and trying to haggle a deal. Has any one had much luck and have you got any tips, I'm usually pretty useless at this but I'm determined to save some money on the contract.