I friend told me about this question and happy to jump on board.
There aren’t necessarily any established Spotify promotion companies out there, and as someone who’s researched this a lot I can suggest you try to get as far as you can without employing a company.
You can google things like “Spotify Submissions” which can find a lot of blogs who have Spotify playlists that accept submissions. You can also try searching the playlist curators and sending them your music, just remember they aren’t bloggers or necessarily music lovers, just people who happen to have popular playlists.
I also, SubmitHub have a Spotify playlist submission section too.
If you did want to use an Spotify promotion company to do it for you, there is a Music PR company in London who I’d recommend here:
I hope this helps!