Reconnect/ repair the integration of the online store with a shipping calculator SDEK

There is a small online store. A bit neglected in terms of attention.



Last year at some point "floated" integration with shipping calculator SDEK. It is expressed that the Site should take in the calculation is the minimum cost of delivery of the order, and began to take one of the most expensive. In the result where it should show 400 rubles 1500 shows (conditionally). The clients pass by.

What is the nature of the breakage I as the Site owner don't know.
Once this has happened in the 2018 year, but the last contractor then fixed it without telling the reasons. In 2019, the year the contractor initially promised to fix, and then generally disappeared. Correspondence with Stacom nothing.

This is basically what needs to be corrected.

Interested in not only the result but the reasons for "failure" to know for the future.

P. S. PLEASE WRITE THOSE WHO CAN HELP SPECIFICALLY FOR the OCCASION.