BRP correction

Dear Experts,

After receiving my BRP card found that there is a mistake in my name printed.
The Last name has been split wrong and joined with my First Name. Had reported to home office via mail <BRPError@homeoffice.gsi.gov.uk> and was asked to return my Passport and BRP card to
Freepost RRYX-GLYU-GXHZ
Returns Unit
P.O. Box 163
Bristol
BS20 1AB

I had used Special Delivery option to send my documents and when I track the mail in Royal Mail it says that "we were unable to deliver as there was no access to the delivery address".

Is sending the documents through Special Delivery not an option.

Please provide your suggestions.