@usered3721 generally Non-Resident Aliens present in the USA file their returns using form 1040-NR and yes there is a flat taxing regime. Also for many NRA, resident in the USA with SSN, there may be withholding by the employer. For those whom are abroad, generally a holding agent collects the withholding and issues a 1042-S for the filer whom uses a form 1040-NR. I suspect that in your case, you bank / broker is probably not aware that you have moved out of the country and that they should have been acting as or using the services of an withholding agent and issue you 1042-S --- they probably issued you 1099s.
So I would suggest that (a) you file US return using form 1040-NR ( not supported by TurboTax ) using SprinTax or similar ( there are many such professionals in many countries ); (b) alert your Bank and brokers that despite your SSN you are NRA and not residing in the USA.
Also note that there may be treaty conditions that are applicable -- so which country are you a citizen of and which country are you in now. You may also want to verify that your SSN is still valid -- because once your visa has been termnated, your SSN that was dependent on the visa , should have been terminated -- may want to chack with SSA or USCIS
Good Luck
