application for certificate of approval

once again i got a letter from the home office saying that they did not recieve the documents that they requested for.But i sent all these documents and got proof with the receipts that they were received at the croydon office.

So i wrote a letter to the home office saying that i had sent the documents required and also sent the reference numbers on the reciepts.its over four weeks i sent this letter to my case worker.till today no reply of either that letter was recieved,everytime i ring the home office all i get is to keep waiting.Any advice please let me know what i should do.