DSl consumables / Forced to buy/pay

This people are ********. They phone you and tell you they want to give you a voucher because it is for promotions of there product. After you tell them various times you are not interested they keep demanding your address so they can send the voucher. When you give the adress they said they are going to send you 2 x 5lt all purpose cleaner and that they give it at 50% discount. When I agree to buy it as a ones off, the 3rd month they send double the order which I dit not want or ask for, they say it was part of the promotion and I can not return it and must pay for it. I told them straid if there is no approved order then no payment will be done. But they keep harnessing me and said I must pay for it.