No, the port is ok. I've tested it from other networks, and my ISP ensures network neutrality
BTW, I can run other coins (eg monero) and the btc testnet works fine for me.
Testnet doesn't use the same port, and neither do other coins. Putting aside the ISP, I've only had this issue once (that was not related to any firewalls), and it "solved it self" after I wiped my datadir and started completely fresh again (don't forget to save your wallet and/or conf file if you go with that).