Santander- Invalid account number help

daraya

I sent letters and token payment to cc companies two weeks ago. Today I received a letter from Santander. They sent my letter+budget back (but no Postal order)saying that my account number i provided (i copy it from previous letter they send me and is definitely right) is invalid and they can not locate it from address and surname. Did anything similar happed to anybody? Is that another trick they do? (Barclay claimed they haven't received my letter and budget but took my £1 payment).