either ebay or amazon, after they sold the device and the money guaranty period even the product still in the warranty period but it seems many responding while we have errors to ask for help. As my likebooks alita, I bought since June 2019. I got two time replacement, first due to the pen in Sept. 2019, the second due to the program in upcoming date no sure when yet as they will respond in one month each.
good luck, Geordie2019!