Solve the VAT problem

Hello!
We are looking for a specialist who can solve the problem with the calculation of VAT.
The situation is:
- There is an online store, a multi-site system is used
- B24 - Business license, box version
- The system has a payment module
- Vat settlement broke in the account
- VAT is considered without the cost of delivery
- The problem is in the B24 core
"Those. support made fixes but couldnt solve the VAT problem
- The bill used to work normally
- Update broke the score
- Changed the file, the spike on PHP, but did not help.

I can provide a more detailed description of the task.
Waiting for your suggestions!