Assume a person is required to file a return in 5 days (and assume such a law exists). The only way this can be done is online. The person, currently living in a distant village under a legal obligation, manages to get an internet connection. People there are not helpful enough to share internet and the internet recharge shop takes ten days to reach. Another person purposefuly uses up his internet pack thereby preventing him from filing the return. Who is liable for this? Practical example: A person detains someone or damages someone's computer rescorce to prevent filing of Income Tax return and also fills the email address of the filer(who needs to file it) with junk emails from forged account to fail be him from finding documents he needed to file Income Tax return present in some emails .
You are required by law to file an income tax return and pay any amounts owed, regardless of your excuse. If a person forcibly and illegally imprisons you and you miss the deadline, you would be subject to the late-filing penalty, however (once you escape captivity) you can sue the assailant for damages, which could include the consequences of late filing. You could also appeal to the Income Tax Department for waiver of the various negative consequences. The Commissioner has the power to grant waivers.
It is not required that taxes be filed online, so lack of a computer or internet connection does not negate the obligation to file a return, it just makes it harder. Your neighbor has no legal obligation to be knowledgeable or helpful, or to provide you with internet service. In some areas, access is generally equal to 1200 baud dialup except for a more expensive service, in which case another person using the internet is essentially "using up the internet". You cannot hold a third party (known or unknown) liable for this consequence of choice of ISP. Nor can you likely hold the ISP liable for your problems, though maybe your attorney will see an angle where the company has breached their contract with you.