[inquisitor]

Then try calling your own number with 99 inserted between the mobile prefix and your individual number.
Be aware that mobile prefixes starting with 016 and 017 are 4-digit while those starting with 015 are 5-digit.

Here are some examples how the mailbox number is being created:
0163/1234567 => +49 163 99 1234567
0178/1234567 => +49 178 99 1234567
01577/1234567 0> +49 1577 99 1234567

You should also know that once you disable your mailbox there will still be a "feature" called "caller info by SMS", which will notify you by SMS about every missed call. Unfortunately if this feature answers the call it will actually be billed to the caller. With Aldi Talk will always have to pay if they try to reach you.