SEO help (serious spam and optimal site structure)

[MHB]

Hi all,

I know "SEO" is a vague word that means endless articles and guessing about Google, but this is shockingly specific due to the scenario I'm in with my forum.

1. Spam - due to an exploit from an old vB add on there was a URL redirect service running for my site that allowed anyone to use it. Spammers knew about the exploit and it made its way onto some lists it seems as the number of links referring to my forum are huge and they are all very explicit. I have shut down the redirect and 301'd all URLs of this type but I still see new ones made daily. It's killing my backlink profile and I need someone with real experience using Google Disavow or something else to help.
2. Site coverage and structure - I also think the rewrite scheme we have in place now is suboptimal and the submitted sitemap is not working well to the point I think Google is just crawling and ignoring if it is on the sitemap. I'm using SEMRush and AHREF to analyze my forum and I see some areas of potential improvement connected to this but want an expert to help.

If you can only offer services for (1) then please write as that is most critical. I was impressed at first honestly at how clever this was because it was running completely blind to my forum. Now that it's blocked and still being used is just annoying and ridiculous.