Here are some suggestions. If you can log into the account please change your gmail password. Choose a strong password. I would also suggest using 2FA that is Google will ask you if you are ok with validating the account with a cell phone number. You can configure gMail to call or SMS you a code so that the system knows it is actually you. Once you are into gMail they have a link buried at the bottom that shows which IP addresses accessed your account. Most of the accesses will be from your computers you own. However, there could be some IPs from IP addresses that you do not recognize. If you find these IPs use a DNS service to locate the ISP and call them (e.g. say ISP Foo) Please tell them your gMail account is being hacked by a user on their ISP and you have logs to prove it. Please give them the IP or IPs and have them take action or tell them you will need to report it as a cyber crime. All The best!
This happened to a family member’s gMail when were on the west coast and I tracked down the ISP somewhere in the MA area. I called them up to report the breach & cyber abuse. The hackers had setup an automated vacation response and had harvested the email address book of the account. They then had a bot setup to send regular emails to the account that would automatically send out a vacation response email to the sender CCing email addresses in the address book. The contents of the vacation response email essentially were stating that the user was stranded in a foreign country and is in dire need of funds. The email was requesting either a wire transfer or entering bank account or credit card details. I am sure many of us have encountered these emails. They are cyber abuse and attempts at cyber theft.
When I changed the password to the gMail account I also deleted the automated vacation response configuration and blocked the email addresses that were sending automated emails.
This Google link might help…
Here is the link at the bottom of your GMail Inbox that will show up Details of the IP logs
When you click on Details in the far right corner you will see all the recent IP accesses shown below
Protect yourself from cyber abuse and cyber theft. All the best.