Thanks Jonova!
So another update for anyone else trying to link - decided to give it on more try and called the number on the back, got the Philippines and the CSR initially advised it couldn't be done and quoted the notes back to me as per the last call... Bugger. I decided to try my luck and gave her the date and time of the call where I was told it would be done (but wasn't), and after a lengthy hold she advised she had been able to process it and transfer the points across and I should see this reflected on the account within 1-2 hours. Fingers crossed! The points have disappeared from the Explorer already but nothing credited into the Ascent yet... Here's hoping they haven't all been forfeited, that would be most unfortunate...
In any case this is my last attempt at linking, if it doesn't happen this time it obviously wasn't meant to be (though I do think I'll probably follow up if my Gateway points just vanish into thin air and try to get them back!)... Apologies for all my posts, but figured it could be useful for others trying to do the same. Good luck!
Edit: The linking gods have finally smiled upon me and all points are now showing in Ascent.