Disappointed with service

Ordered 2 items with them on the 1st of December, received just part of my order, was assured in writing that they would deliver the week off the 20th, since then there has been no movement on my online account with them and I receive a 404 error when attempting to click on the item for delivery. Have mailed them several times and have had no response from them since, very disappointed with there lack of customer service. I'm sure that they will be debiting my account on the 2nd payment soon which means I would be paying for a service I have not been receiving. I am also sure that they won't be amending my contract in accordance to the time frames of delivery.