Try running this example
import re
data = """
RTGS-VEERPAL/KARBH13267941306
TO STAMP PAPER CHARGES
2013
1348
By Clg/33790/ICICI/DELCTS1/166
RTGS-KUSUM TOMAR/CNRBH13271696922
RTGS-SHRI BALAJI BUILDHOME PVT /KARBH13294076078
By Clg/956226/AXIS/DELCTS1/171
"""
pat = re.compile(r'(?<!\w)\d{4,}')
for line in data.split('\n'):
if (m := pat.search(line)):
print(m.group(0))
To get that solution I went to https://www.autoregex.xyz/ and entered the description "four or more digits not preceded by an upper case letter".