Password Length Limitation?

[Banaanhangwagen]

If I understand it correctly, the password is 25 characters long: 20 lower case (that you know) and 5 digits at the end (that you don't know)
The -m for a 7z is indeed 11600.
The hash is correctly formatted in a text-file, that you call hashcat.txt

Try:
hashcat -m 11600 hashcat.txt -a 3 your_20_lower_case_characters?d?d?d?d?d