BiqQuery find decimal point in String and remove everything are decimal (including Decimal)

I am using BigQuery and need help finishing my query.

We have a dataset of Order numbers that have a few issues (This is what I want to achieve)

I can get the "@00" removed but I can not get the decimals removed to get a single OrderNo when I have a decimal included. (They use the decimal for sub Jobs)

SELECT 
 ORDERNUMBER, 
 Case 
 when regexp_contains(ORDERNUMBER, "@") then regexp_extract(ORDERNUMBER,"(.*)@" ) 
 when regexp_contains(ORDERNUMBER, ".") then regexp_extract(ORDERNUMBER,"(.*)." )
 else ORDERNUMBER
 end as Outcome
 FROM `JOBHEADER`

I tried escaping the "." with \ and / but I have no idea how to find it using regexp