Just a quick update that my unconfirmed transaction were showing again after Coinpot actually resent the payment using a Segwit wallet on 22-23/12. The transaction was just confirmed today which means it took a total of 5-6 days which wasn't so bad if you didn't have to pay for the transaction fees. So the timeline actually goes like this;

17/12 requested payment and was processed on the very same day
20/12 payment unconfirmed for 3-5 days
either on 22 or 23/12 payment cancelled as they switched over to a segwit wallet and resent
transaction showed up as unconfirmed in wallet again
28/12 transaction confirmed and payment received