Before you blame your ISP check out this linkhttps://pentest-tools.com/discovery-probing/udp-port-scanner-online-nmap#. Select the option to enter your own selected port range, enter 5060/5061, answer the simple math question to prove you're 'human' and START. You should receive this as a (partial) result; PORT STATE SERVICE
5060/udp open|filtered sip
5061/udp open|filtered sip-tls