NSMutableattributed string not working for substring

Question

-(NSMutableAttributedString *)getAttributedStringforString:(NSString *)totalString filtertext:(NSString *)filtertext font:(UIFont *)titlefont backgroundColor:(UIColor *)bcolor foregroundColor:(UIColor *)fcolor
{
    NSMutableAttributedString *attributedString = nil;
    NSDictionary *filterTextAttribute = @{NSBackgroundColorAttributeName:bcolor, NSForegroundColorAttributeName:fcolor, NSFontAttributeName: titlefont};
    attributedString = [[NSMutableAttributedString alloc] initWithString:totalString];
    [attributedString beginEditing];
    [attributedString setAttributes:filterTextAttribute range:[totalString rangeOfString:filtertext options:NSCaseInsensitiveSearch]];
    [attributedString endEditing];

    return attributedString;
}

I am applying NSMutableAttributedString for filtertext in totalstring if filtertext is totalstring then the above setattributes is working otherwise its not working for substrings