My 2018 federal tax refund was rejected but was accepted about 6 months ago,why haven't I received my refund

[DoninGA]

After the tax return has been Accepted by the IRS (meaning only that they received the return) it will be in the Processing mode until the tax refund has been Approved and then an Issue Date will be available on the IRS website.
See this IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions

Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
When calling the IRS do NOT choose the first option re: "Refund", or it will send you to an automated phone line.
So after first choosing your language, then do NOT choose Option 1 (refund info). Choose option 2 for "personal income tax" instead.
Then press 1 for "form, tax history, or payment".
Then press 3 "for all other questions."
Then press 2 "for all other questions."
- When it asks you to enter your SSN or EIN to access your account information, don't enter anything.
- After it asks twice, you will get another menu.

Press 2 for personal or individual tax questions.
Then press 4 for all other inquiries
It should then transfer you to an agent.

[Bsch4477]

Refunds are taking a very long time. You will have to contact the IRS since TurboTax has no control over your return once it’s accepted by the IRS. 

[xmasbaby0]

Please explain that.  If your 2018 return was rejected when it was e-filed in 2019, then the only way you could have filed it in 2020 was to print it, sign it and mail it.  Did you do that?  Or did you use the wrong software and e-file a 2019 return with 2018 income on it six months ago?