Not a solution but perhaps a workaround:
Telekom Deutschland not only allows SIP over UDP but also SIP over TLS. In that case, you have one persistent connection and do not go for DNS anymore. Therefore, not every call but just your initial registration is load-balanced via DNS-SRV.
However, because Telekom Deutschland offers only TLS 1.2, you have to go for method=sslv23 in your pjsip.conf (if you still use OpenSSL 1.0.2 or lower). There is a deticated thread for more options/details about that…