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| *Salary 1 (1/2 month) - 500 CHF *
December 13th month (1 whole month, plus pro-rated 13th month) = 1125
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Half of November plus December is 1/8 of the year so combined payout should be, and is, 1/8 of 13k or 1'625.

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| * June 13th month (1.5x salary) = 1500*
10 x normal month = 1000
Final 2 weeks pay in November 2019 = 500
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You can't end a job contract in the middle of the month unless it's of fixed duration, which I assume to apply to your contract. So the total pay for the remainder of the fixed-term contract should be 7/8 of the annual salary as 1/8 has already been paid.

7/8 of 13k is 11'375. That's the total you're owed for 2019.

In your calculation the 13th salary for the final 4.5 months is missing, that is 3/8 of the 13th salary, which is 375. However you seem to count 11.5 months (10 months plus June including half the 13th plus half of Novemer).