false advertising, refusal to refund

Once ordered and paid for, They keep letting you know that one item is out of stock. next day someone else lets you know that another item is out of stock... Also, the item, described on the advert, often is not what is described. eg, support stockings, pictured as knee length, is ankle length...and a vacuume machine, advertised to include 15 special bags, and only 5 were in the box. They refuse to refund or return the items that were incorrect, and say I have to return it for 15% penalty, and i would have to pay for courier... and the items that were out of stock, they want to give you a voucher, instead of a refund...I respectfully asked for a refund, but they refused.