GA4 account looked into

Could we please have some advice on you looking into the following for us,
We are working with a 3rd party marketing company who we have been with for nearly a year. We noticed at year end 2024 that the figures they were presenting for the different platforms: Google analytics and Meta were adding up to be much more than the total conversions from our website for the same period. Not even taking into consideration our email marketing figures (Klaviyo), GA4 and organic.
After this they thoroughly investigated Meta and Google ads and found there was over reporting happening. They are now very confident that this is not happening anymore as of mid Feb 2025.
We can however see that for March so far similar is happening again leading us to jump to that this has not been fixed. They have assured us there end this is accurate and we need to look into the other aspects for discrepancies like Klaviyo and organic – GA4.
We set GA4 up ourselves and this is where we would like to use your knowledge. Are you able to look into our GA4 account and check this is set up correctly, we know this cannot be correct (if there Google analytics and meta is correct) AND paid social (Klaviyo) is way out conversion and conversion value wise. Same for organic, and everything within GA4.
If you are able to advise on this we are very happy to pay and have you look into this,
Many thanks, Charlotte