Just call the SSN office and confirm they dont see any application already in place and then get an appointment to go in person and file a new application. Its an easy one page application form with very few details. If they see the application based on i-765 then you can follow-up for its status.
My sons EAD came thru in late oct and we waited for 2 weeks and called ssn office to inquire about the status as we selected for SSN issue in the form. They confirmed they dont see any application submission based on EAD approval. So then, they setup an appointment for in person and we went and showed all the necessary docs like passport, h4 i797, ead card, school id, etc. After 7 days he got his SSN by mail. Now, I have called IRS and asked for appointment to convert ITIN to SSN and will be going there mid of this month.