Extremely upset and frustrated

I ordered an item which they sent was incorrect, I requested the right one to be replaced but they said that it has gone up in price so want to give a credit or a refund which is not all the money I paid, I tried calling the company but it doesn't go through, I wrote to the company on Facebook and Instagram but haven't received any feedback, I want to get my item replaced with another company that they have on the website and it's cheaper but I cannot get hold of them, because if I reorder then I must pay for delivery again, I am not prepared to pay again for their mistake in sending the wrong item, this is terrible service for such a big company, please be careful when dealing with this company