"Im worried that if I block proxies/vpns Ill also stop real users" - it will. Lots of people use VPNs for a large number of reasons (including privacy and circumventing censorship). Blocking a VPN won't be enough either, because a good chunk of internet spambots are computers owned by regular people that are part of a botnet.

If you're using Wordpress, there's anti-spam plugins that trick simple bots. There's one that uses hidden form elements, for example. There's also better, but IIRC paid plugins as well. There's also always going to be attempts to get around it. Fighting spam has been an ongoing battle since submitting stuff was a thing. As long as you want anyone to be able to access your platform, anyone will also be able to submit spam.