Are you actually on call? Like, do you have a beeper next to you? Will you suffer consequences if you don't respond? There is "oh things aren't going great I guess I need to cut my vacation to Austria short" and then there is "I cannot go out for drinks, I cannot take a nap, I must have my company laptop with me and with good Wi-Fi" on-call. Oh, and for the latter you're getting paid a few hundred an hour at best. Just putting that out there.