Why is my Amex balance due always so high?

grumbler

Farr said:

I've set my payments up as direct debit so I always pay in full. My refunds usually are very quick with Amex

It's the timing that matters, not the speed.

this is why I didn't understand why I get charged a high amount in the end. 

Let's say £100 payment was made on the 20th, the statement produced on the 21st with £200 balance and the refund credited on the 22nd.  If the refund isn't counted as a part payment of the full statement balance (that seems to be the case with Amex), the full £200 amount will be taken on the due date regardless of the refund. However, the refund does reduce the next statement balance and the next payment accordingly.

I'm assuming if I were to ever close my account Amex would send a cheque for any outstanding refunds once I've already settled the balance due.

Yes -  for any outstanding credit balance. If you don't make any new purchases after the last statement, the balance will be a result of refunds only.

Jami74

Farr said:

I've never tried putting a spreadsheet together but maybe it's about time I try.

I literally only keep the credit card to build a good credit history but it was much easier keeping an eye on my money when I was spending from just the one bank account.

If you don't know how to do a spreadsheet, even handwritten would work, literally just a tally of what goes in (your payments and refunds) and what goes out (spends and charges/interest).

If it's just for building credit history maybe go back to spending on debit card from your bank account and use the credit for one or two regular spends each month (eg groceries or commute), rather than every spend. The fewer the transactions, the easier it is to reconcile.

Angelica123

I think the thing to remember is that there is a lag between bills being created and when direct debits are taken. I have occasionally ended up in positive credit if a refund has occured after I have already paid bill (and I haven't yet spent much in next monthly statement). But it just means I pay less in subsequent months. 

You mentioned being confused by terminology. 
Available credit: is self explanatory. It is the amount of credit available to spend. It will be credit limit minus any credit (eg spending) that has not been paid off
Previous closing balance: was balance that you were billed at previous month's statement
New Credits: should ideally equal be same as the previous closing balance if you pay off a CC in full. But it is any positive payments to card which includes payments you made (and would include refunds). 
New Debits: would be any new spending since your last statement
Closing balance: is the amount you are due to pay that month which is calculated by previous closing balance - new credits + new debits. 

For you, it may be easiest to stop spending until you are at 0 balance and then only buy one or two things a month so you can track more easily.