Generally speaking, charity gifts generate a reduction in tax, but no payment if you do not pay enough tax to benefit.
However, as 2018 was, exceptionally, an année blanche with no tax on most regular forms of income, tax could only be reduced if people owed it on certain “one-off” incomes.
Therefore, so as not to lose out, you should have received a payment in September 2019 if you had no such taxable incomes. We would suggest querying this with the tax office.