IP address from ISP

Solution 1:

Is it possible that ISP didn't provide real public address for me but instead it gave me an address being a result of PAT?

Yes. Many ISPs now use Carrier-Grade NAT (although there are still many which don't).

For example, if your router shows that its ISP-assigned address is from the private 100.64.0.0/10 range, that's definitely an indication of CGNAT.

is PAT on multiple intermediate rotuers possible?

It is. To the outside, NATed packets are indistinguishable from normal ones – they can be NATed again in the same way. There are many real-world examples of double or even triple NAT occuring accidentally and intentionally.