vb.net / sql server code refactoring

I am looking for a VB.net and SQL server expert to refactor and fix an issue I have with my code. Currently, the piece of code has got inline SQL written for inserting record in SQL. the problem I am facing is when two people race to insert the record, it inserts same record twice and for one purchase two invoice gets generated. I need to fix this issue and to detect a deadlock while this happens. so you need to refactor this code to rewrite the piece of code to check the record exists or someone else has raced to insert the same record, if its inserted, you have [login to view URL] an exception or if not insert it. also u need to write a logic to check for deadlock. Solution u provide could be written as stored procedure as well. let me know if u have any questions before bidding. thanks