Order B is paid for and delivered? The value of which was £20 and you’ve paid £20. No issue here, so disregard it.
Order A was placed and paid for? You’ve had confirmation from Paypal and the moneys left your account?
Order A has not been received?
Was confirmation of Order A received by you? What about a confirmation of despatch?
Paying by debit card doesn’t give you the same protections as paying by credit card.
If you’ve received confirmation of Order A and notice of it’s despatch then it’s clearly been lost in the post. The supplier should send out a replacement – and claim for the lost goods from the courier themselves.
If you can’t get through on the phone then you need to write to the supplier (e-mail and post) asking for replacements to be sent.
If you’ve not received confirmation of Order A then it sounds as if there’s been an error in their system. Again, write confirming that you paid £70 for items xxxxxxx and that you’ve not received them. Ask that they be posted to you.
Aternatively, you can write canceling the order and asking for your money back. You’d be entitled to it. Paypal may have an automated mechanism to do this. I know they don’t with personal transfers but for commercial transactions – ie where the vendor uses Paypal as their cashier – I think they do.