After I searched the PayPal community forum, for a while, I found 2 solutions. The first solution - to clear the cookies/cache from the browser - I did that and I still got the error message (even after I changed my password for a second time, before that). The second solution - to delete that PayPal account and open a new one - I didn't try this solution but maybe I will consider it if I can't restore my account. If possible, I will wait for a while, if someone has another solution to my problem, for my PayPal account.
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