The insurance company issued the seller for one year

The insurance company issued the seller for one year

The insurance company issued to the seller a one-year bank guarantee for securing B.´s obligation to pay for the goods purchased from him in installments.
Two months later, the seller demanded that the insurance company repay the debt to B. The insurance company refused to pay, because B. had presented her with indisputable evidence that he had paid the seller completely.
Should the insurance company pay? Justify the answer.

Additional information:

After payment you will be available a link to the solution of this problem in the file of MS Word. It should be noted that the problem solutions put up for sale were successfully handed over in the period 2003-2018 and could be outdated. However, the general algorithm will always remain true.