This looks wrong:
strSelect = "Select * From Customers"
strSelect &= "WHERE ID = (ID = @TXT_Cust_Record_ID)"
But that won't affect the update.
Which means we can't tell - we don't have access to your DB, or to the values you are passing to it, particularly the
@TXT_Cust_Record_ID
value.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. If you don't know how to use it then a quick Google for "Visual Studio debugger" should give you the info you need.
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why. When you know exactly what is being passed to SQL, and have checked in yoru DB to see if there are any matching records you can start thinking about why it's a problem. I'd guess that no rows match the ID value, but I don't have any access to data to check.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!