Account that is not correct

I ordered goods on line, when I received my package there was only 1 item inside, a inner. I contacted them, told them that I did not receive curtains, no problem they will credit my account, I ordered again, towels, tupper and a duvet set. I only received the duvet set. When I told them they say they will fix it, next morning someone else calls again, and so it goes on. They want payment for stuff I did not receive, when I explain they say they will get back to me. I have never received a statement, and the people is so rude it is not even funny, they say they will fix it, but nothing happens, I dont know what to pay, and they tell me the amount, but it is for stuff I did not receive.