Hello,
Old textbox structures don't use the same structure for text contents than 'normal' content, such as paragraphs, tables and others. To replace texts in textboxes you need to use the raw option available in replaceVariableByText or rawSearchAndReplace.
For further support, please send to contact[at]phpdocx.com the username or e-mail of the user that purchased the license and a DOCX sample, and we'll generate a simple code to illustrate how to replace that content.
Regards.