Can’t get program to run properly

[buran]

it's not clear how you run your code and call functions you define in the snippet
then you have defined get_customer_info() function but it does not return anything, so even if you call it at some point it will have no effect
also you have get_customer_info argument in the signature of letter function. Note that it's something different from the function of the same name defined before that. You never use it in the body of the said letter function. all the variable like name, street, city, etc. would not be defined when you try to use them