Should I refuse the invitation to review a paper which I recommended for rejection? What should I do if I suspected who wrote this paper?
It's fine to review a paper that you have previously recommended for rejection (assuming you gave reasons rather than just dismissed it). The editor took your comments into consideration when deciding to seek a revision and I would expect the authors to respond to your concerns in their revision.

However, the second question is definitely grounds for refusing. The editor may wish to include you because you raised concerns and are in the best position to assess the extent to which those concerns have been addressed, and you may be incorrect in your authorship guess.

What you could do is an email to the editor along the lines of "Since providing the previous review, I have come to believe that PERSON X is one of the authors and I have a conflict of interest if that is true. Unfortunately, I must therefore decline to review unless you can assure me that PERSON X is not one of the authors."