Trouble with notice period in part-time job

I started a part-time job as a working student in a public library two weeks ago, on a 30-hour monthly contract. Before signing, I provided an 8-hour weekly availability (“Kannzeiten”) for scheduling. The contract makes no mention of a probation period (“Probezeit”).

The day I signed, I was told to enter my name into an open Excel schedule shared by all staff, filling in my available hours. However, most slots were already taken. I added my name to a few cells, but by the next day, they were removed, and the slots were filled. The supervisor said this was a “technical” issue. Last weekend, I tried to schedule my November hours within my available times, but again, all relevant slots were unavailable. I mentioned this on Monday, as it makes it impossible for me to reach my contracted hours.

I submitted a resignation letter but was informed of a 4-week notice period, ending Dec 15th.

Questions:

1.  Is a 4-week notice standard in this situation? Shouldn’t it be 2 weeks if there’s a probationary period?
2.  Could the lack of available hours in my specified schedule be considered a contract violation, justifying an “außerordentliche Kündigung” (extraordinary termination)?

Any advice would be greatly appreciated!