Can't trade, can't withdraw - GDAX ripping me off?

Hoping someone can help.

I signed up to GDAX a couple weeks before Xmas and made a € deposit via SEPA.

The transfer went through, and the funds are showing in my Coinbase EUR wallet.

But. When I try to buy BTC or ETH - 'Insufficient funds'

When I try to withdraw the cash via SEPA to my verified account (it shows as a SEPA destination) - 'Insufficient Funds'

I've tried using smaller amounts in case I'm not factoring in fees etc - doesn't matter how small a transaction I try - same error.

I don't understand what's happening - the balance is there and clearly shown - why can't I access it?

I've emailed the support team 3 times - no response after 5 days. I tried the support number earlier but gave up after holding for an hour (I'm UK based)

Are GDAX / Coinbase fleecing me?? Can anyone help?

Thanks

Greg