Wrong information about retirement contributions on W2

My employer wrongly classified my 403b contributions as 457b contributions on W2 and did not deduct the $18,000 in contributions from my wages in Box 1 (but did take them from my paychecks) so I am going to owe taxes on that $18,000. I tried to contact the HR department but I work at a College and it is closed due to Covid-19. How can I get that corrected and should I file now and then file an amended return later?  The error changes my refund of about $3600 to owing $850. Thanks for any help.