[mtmail]

You can lookup and write to their data protection officer. Often that goes to customer support and then gets company-internal redirected, sometimes it goes to the legal department directly. If it's a GDPR complaint then they have 4 weeks to reply. When I last used it after two weeks I sent a follow-up, it was a copy&paste from the local data protection agency (in my country it's per state and I had to lookup which one is responsible for their business). The wording was something like "Based on <paragraph> please delete [...] information or give me a justifiable reason why you can't comply". My account got deleted almost immediately. Knowing the regulation helped.

That said I'm sure Deezer in their terms of service allow for termination of any account. If you request partial deletion of information and they can't provide that they will terminate your account. And for financial/tax law (which overwrites GDPR) they might still have some of your info stored in a different system for 10 years.

It comes down to how patient you are, how many letters you're willing to send.