Can't create new Giveaways

Yes. Wait for support to answer those tickets.

you have to create a support ticket, and kindly ask the mods to manually increase your giveaway slots because deleted giveaways block 1 slot / each.

here's how the maximum of giveaway slots is calculated:

3 + rounded_down( "number of successfully delivered giveaways" divided by 3 ) - "number of deleted giveaways"

in your case:

3 + rounded_down( 4 / 3 ) - 4
= 3 + ( 1 ) - 4
= 0

If you've already created a support ticket, you can bump it once a week, so it gets send to the top of the ticket list (like a trade thread on steamtrades after a bump)