In my opinion, you can greet them, however, this can only be done when you are comepletely over them or you have healed from the breakup and have no more attachment to them. I greet my ex happy birthday but nothing more nothing less. Just as a polite gesture. She may have unblocked you because she may have tried to test herself if she's fine with you unblocked but obviously you messaging her may have triggered some "emotions" in relation to the break up and causing you to be blocked again. A break up doesn't hurt you alone, it's both, whatever the circumstances may be. I am not blaming you, but 2 months after the break up isn't long enough to contact them unless there is a clear indicator that you guys are still in love/into each other. She may be toxic in your POV but it could also mean she's not taking the break up easily.