Mail merge from Office support- troubleshooting

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Job Description

I am trying to do a mail merge from Excel into a pre-done Word doc; however, when I modify the address block or greeting line, I get one of the two as it changes both:

John Smith OR Mr. Smith
123 Main St. 123 Main St
Anywhere, USA Anywhere, USA
123456 123456

Dear Mr. John Smith, Dear Mr. Smith,

It's been correct in the past, so know it can be done. I've tried starting over again with both files with no success. The way it should be read and merged is the following:

John Smith
123 Main St.
Anywhere, USA

Dear Mr. Smith,