Commission claw back Question

[porscheman30]

I joined a company doing a sales job and was paid a draw (guarantee for 3 months) while I got up to speed and started selling their solutions.
I got three monthly payments of around £3k (total £9k) but if course paid tax on all my earning( so cash I took home around £6k after tax rough guess). I have paid one payment of £3.2k back to the company in commission to date.

My question is, If I leave tomorrow do I owe them £6k or do I own them £6k less tax something in the region of £3.5 to 4K. who is liable to pay or claim the tax back? Also I do not have the cash to give them in one lump sum, would they be happy with a payment plan, or can I expect some legal action?

thank you for your help.