Yahoo customer service phone number - https://help.yahoo.com/kb/account/yahoo-support-number-sln27069.html
As the article above states If you see what someone claims is a Yahoo Customer Care phone number posted online, whether it's on Facebook, Twitter or another social media channel, a web forum, or on a help site that claims to provide Yahoo tech support, it's not Yahoo, and it's not a Yahoo phone number!
Support from Yahoo is always free. If you call what you think is a Yahoo customer service phone number and are asked for credit card, banking, or account login info, end the call immediately.
What this person you called said was bogus and was only a way to get you to buy whatever software they were trying to push.
You can try the following help articles for assistance
Accessing Yahoo! Mail on mobile devices - https://help.yahoo.com/kb/mail/SLN8223.html?impressions=true
Fix mobile sign-in issues - https://help.yahoo.com/kb/SLN2617.html?impressions=true
Why am I not receiving messages on my mobile device? - https://help.yahoo.com/kb/mail/SLN6351.html?impressions=true
Generating App Passwords - https://help.yahoo.com/kb/mail-for-desktop/generate-one-time-password-sln15241.html
Error: "Mobile Locked" - https://help.yahoo.com/kb/SLN5764.html?impressions=true
Network connection failure when accessing Yahoo Mail - https://help.yahoo.com/kb/SLN22197.html?impressions=true
If the articles above were unable to help you then start here - https://io.help.yahoo.com/contact/index?page=home&locale=en_US
Select "Mobile" for Product.
Select "Yahoo Mail App" under Topic.
Select "How to set up mail app on android " under Subtopic
You will see the support options available under the Recommended Options column.