To process this "digits to word" operation, you can use Microsoft "Recognizers-Text" features.
There is a github project available here: https://github.com/microsoft/Recognizers-Text
You can see a sample of the behavior for Numbers here: https://github.com/microsoft/Recognizers-Text/tree/master/.NET#microsoftrecognizerstextnumber
With that, you can replace digits with their word version. It can be used in several languages: .NET, Js, Python, Java...