How to overcome Negative SEO

My client site was blasted with spammy links and it is continuing. Currently there are around 20k link and it grows on. I hope google might found it as an attack but how can i improve its SERP? Current position is #11 for a keyword, i would like to bring it to #8 or #9. Will authority backlinks worth(work) now? Or better to concentrate on social and other factors instead of authority link building?

Google has link disown tool which you can use to remove bad backlinks.

I just used it to day to remove 4 backlinks that were clearly bad.

Edit i am new so i cant post links but just search in google "Disavow tool google"