Send a follow-up email to confirm whether the notice has been received or not.

Make sure to CC in relevant departments like CTO/HR/line manager.

If that follow-up email is also ignored/unnoticed, you may try sending a certified letter to your company address.

In my country (Spain), there is a service called "burofax" where you get not only confirmation that the mail has been delivered, but also the contents of the letter are registered, so the company can not argue that the contents were different. I couldn't find a similar service in USPS, but still with certified mail you'll get at least confirmation that somebody received the letter.

Once you've attempted all reasonable means to contact the company about your resignation, and if you still get no reply, you may have to organise the off boarding yourself. Keep making emails and contacts to the relevant departments, like HR or logistics for handing off the company equipment. If nobody is willing to give you instructions, you may also have to send the equipment through certified mail. On your last day if still nobody replied to any single mail, send a last mail confirming all the offboarding steps you have made, offering your contant information (for hand over purpose only), and leave.

With the evidence of all the attempts to contact the company and with you complying the notice period, you have strong evidence to defend you not showing up after your notice even if the resignation was not acknowledged/accepted, then the next move will have to come from the company itself.

Send a follow-up email to confirm whether the notice has been received or not.

Make sure to CC in relevant departments like CTO/HR/line manager.

If that follow-up email is also ignored/unnoticed, you may try sending a certified letter to your company address.

In my country (Spain), there is a service called "burofax" where you get not only confirmation that the mail has been delivered, but also the contents of the letter are registered, so the company can not argue that the contents were different. I couldn't find a similar service in USPS, but still with certified mail you'll get at least confirmation that somebody received the letter.

Once you've attempted all reasonable means to contact the company about your resignation, and if you still get no reply, you may have to organise the off boarding yourself. Keep making emails and contacts to the relevant departments, like HR or logistics for handing off the company equipment. If nobody is willing to give you instructions, you may also have to send the equipment through certified mail. On your last day if still nobody replied to any single mail, send a last mail confirming all the offboarding steps you have made, offering your contact information (for hand over purpose only), and leave.

With the evidence of all the attempts to contact the company and with you complying the notice period, you have strong evidence to defend you not showing up after your notice even if the resignation was not acknowledged/accepted, then the next move will have to come from the company itself.