Two suggestions if there is no "network" solution to the stupid ISP:
#1. Get an RTC board for the pi so that date/time is remembered over reboots and doesn't have to depend on NTP updates.
#2. Try setting the router IP as an NTP source; as some/many routers will respond to the request. As long as the router's internal clock is fairly accurate on current time the pi will get a time/date that's close enough for YouTube etc. to work and you have a workaround. You can also get an NTP server app for other machines in the house Win/Linux with a persistent (if not accurate) clock to pull the same trick.