Barclays Partner Finance review: store card debt

I have been trying for the last 2 week's to set up a repayment plan with them. So I can finally clear this debt I have with them.
I gave them my income and expenditure. And they are now saying I have to fill out another huge form with more detailed information of it all.
They told me they received the first one and it would be set up in 7 days. 2 week's later they're making me jump through more rings of fire.
I would like to clear this debt but they are the ones stalling.

They also cause some get a default on my credit file because they failed to update my address in 2014. Which meant all mail went old address notifying me of that payment plan ending.

I am thoroughly destraught by their actions both then and now. I want a clear this debt and they keep making it difficult for me to do so. What's more, I now have to wait 2 more years before I am able to get a decent mortgage deal.

Please look in to this for me and help me sort this.