Some background will help me explain myself better - I maintain a software system that is used by the sales team. A sales person enters some data, then some complicated computations are done, and a set of values is produced.

For simplicity sales provides some [Input], I maintain a set of functions F(x), to where `F([Input]) = [Output]`

Another person was assigned to update some formulas for a part of the project. They gave me some formulas `f(x)` and they expect result `y`.
When I run *their* new formulas on expected [Input], I get result `z`, and not `y`. z and y are supposed to be Very similar, since it is a different way of computing values that is supposed to improve accuracy.
However, the values are coming out wildly different.

On my end, when testing it, the sales [Input] is fixed, so I cannot magically change it. The given formulas produce the wildly different and bad values. I thus suspect that the formulas given to me by this person are wrong.

The persons *insists* the error is in my code, and keeps telling me to "check it". I grow increasingly frustrated, since I cannot pull out values out of thin air and I maintain that the formulas are wrong. The only other area that's wrong could be that we are looking at different initial [Input] test data, but that does not appear to be the case.

So the person keeps telling me to check my code, but in this case, the code *is* their formulas and they gave me the formulas. I am not sure how to get through to the person. and from my previous dealing with them I started to suspect that they may not be fit for the job. At least in the sense of collaborating effectively with other people.

I've also asked the person multiple times, to provide me the exact values that they use in their formulas to come up with a different result, but they keep pushing back, not supplying me with values, and telling me things like "you will be confused", or sending me screenshots of excel file with the results, but not the actual Excel file, or the formulas. This is again weird to me - if I asked you to supply me with your formulas and computations and to "show me your work", would you ... send me what I asked for, or would you send me a screenshot of your final result without showing any work? In my case the person is doing the latter.

I also did not touch on how incredibly aggravating all this is too me - what was supposed to be a very simple formula update, which I have already completed, is turning out into a lengthy turmoil of a project, with the person not helping me complete their project, and telling me to "check my code", when it is fairly clear to me that "my code" is not the problem here. I am thinking the problem is the person's work, and lack of support they provide me when I am trying to figure out what the actual problem is with their work.

Also I have not been able to get through to the person very well. It's like they exist in their own world, and I find myself trying to put myself into their world to be able to communicate with them (i.e. when they are not providing the background for their formulas, I attempt to find work-arounds instead of demanding they provide me with all the details, because so far my attempts to request those fell short).

How do I get myself out of this hell?