Missing items, issue ongoing for 12 weeks

So I accidently replenished Item A when in fact I sent in Item B (both items on my catalogue) for 12 weeks now, numerous phone calls and emails they have still not been able to sort the issue out. The stock is worth a lot of money to me and this constant going round in circles is getting very frustrating now. on multiple occasions they have said they have got the stock and will correct the issue and add them to my inventory. I'm still waiting 12 weeks later.

Im thinking of making a claim through the courts, if I were to go ahead. Can i add my admin costs and ask for some sort of recompense for the time this is taking.