Which of the suggested approaches did you try? If shutting down all the mongos processes wasn’t sufficient, I expect shutting down all mongod and mongos processes per the MongoDB 2.4 tutorial link should have worked.
We don’t have a job category in the forums at the moment – I would look to your normal channels where you would hire trusted consultants or experts.
If you are going to hire a specialist, I would get their advice to plan an upgrade to a modern and supported version of MongoDB. For example, MongoDB’s Consulting team has a Major Version Upgrade package.
For some approaches to consider if you want to fast track upgrading through multiple major versions, see Replace mongodb binaries all at once? - #3 by Stennie_X.
Regards,
Stennie