How to fix reply to setting in settings > accounts so that replies come back to my default email address?

[Harris]

Recently, when recipients of my emails hit "reply" the "To" field of their email, which should contain my email address, would be blank (as if their email program had no address to which to send the reply).

I don't understand why this is happening as my account settings have not changed and had been working correctly for years - I have been using a valid alias email address (from my university) as my "reply to" address for many many years in Yahoo mail with recipients having no problem in responding to my emails sent from that alias address. I suspect this recent development may have something to do with recent changes to the Yahoo Mail! website.
For example, I tried going into settings > accounts and editing the affected account, but it did not resolve the problem. I then tried adding a new account, but the Yahoo website produced an error indicating that I should contact customer care.
I cannot find a way to contact customer care for this type of issue.
I would appreciate guidance on how to resolve that my emails "reply to" field contains my email address, or a means of contacting Yahoo customer care to inform them of this bug so that it can be resolved.
Thank you.