for 2018 did you get an acceptance e-mail. the only way to check if it was filed is to see if the IRS has a tax return transcript.
https://www.irs.gov/individuals/get-transcript
if not then because Turbotax says rejected, you never successfully e filed. in turn this means you must file an original return. to finish/change your return you'll need desktop software. most likely you haven't paid your fees for 2018 which would prevent downloading.
Contact Customer Service
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https://support.turbotax.intuit.com/contact
800-446-8848
