Theorie:

To speak about product problems , you need the appropriate vocabulary.
 
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Refund - an amount of money that is given back to you, especially because you are not happy with something you have bought;
 
Replacement - the thing or person that replaces something or someone;
 
To be satisfied - pleased because you have got what you wanted, or because something has happened in the way that you wanted;
 
Receipt - a piece of paper that proves that you have received goods or money;
 
Warranty - a written promise made by a company to change or repair one of its products if it has a fault;
 
Return - to give, send, or put something back where it came from;
 
Make and model number - a group of numbers that represents the product.
 
Examples:

If you want to return a product, you must have a receipt.
  
Our company offers a refund or replacement.