You do not state what operating system you are using, the language, most importantly your character set, and HOW the .xml file was created. Just stating .xml is not precise enough. LibreOffice Calc will expect .ods files written using Unicode.
What do you mean by having problems with SLASHED ZERO? Is it Latin Capital O with stroke Ø (U+D8) or Latin small o with stroke ø (U+F8) or even Circled division Slash ⊘ (U+2298)? It could be a possible clue is the character set setting. They are all Unicode but not found in US-ASCII. If it is just the circled division this is only in full unicode.