Whoa, hang on.
Your older child is a son? Therefore this:
I Wanted a night alone wiht my daughter and jsut becuse i didnt want to spend the nigt with ex she stopped me seeing OUR child.
- translates as you wanting to take a 4-week old baby from her mother, possibly overnight?
Then that is your problem right there - both legally, and in every possible logical, practical and emotional sense.
Yes you have a right to have a relationship with your child.
However, there is NO WAY a court will order that a mother and baby should be separated at all, for any length of time. The most that is likely is that she would be required to allow you access several times a week for an hour or so, with her present. IT'S A TINY BABY. They need their mothers, it is in their absolute best interests not to be separated and that will be the case for some time. Overnights are a long way off indeed!
If this is what has happened, then not only was she right to refuse you but you've done yourself no favours acting so aggressively when she has just given birth. You risk coming across really badly in court. 4 weeks post partum she won't be obliged to go anywhere, much less mediation!
You are likely to have more, better, and more stable contact with your daughter by changing tack. Remember - it isn't actually in your daughter's interests to be away from her mother right now, at all. Do you like the idea of your daughter being distressed so that you can 'win'? Hopefully not, so try thinking about this from another perspective. Be onside. Offer help and support. But absolutely back off from the 'It's MINE too' approach with a mother and her new baby. That will not end well, in court or out of it.