This is Joanna from LOUD (I found your email on your website) and I think our service might be something interesting for you.
Loud scans the whole Internet for Free Spotify Collaborative Playlists that you can add your songs to.
Yes, you do not have to ask anyone for permission or pay for placement. You simply open a playlist in Spotify client and drag and drop your song there.
We currently have over 1000 playlists that we guarantee you can add your songs there and we will monitor your songs positions on them. LOUD gives your more REAL Spotify listeners and increases signals to Spotify algorithms.
You can sign up for a free version that gives a few playlists a day and when you’re ready you can upgrade to get access to all playlists.
Give it a try at https://loudloud.com/
All the best,
Joanna from LOUD