Did you use Prolong Subscription within MFPro and then pay for it expecting an email, or did you use Buy Subscription with an old key on this page:
https://marketfeeder.co.uk/buy/ ?
I believe you can use your previous key in the activate box withiin MFpro or when you try and open MFpro with an expired subscription, once you have made payment. I can't guarantee this will work for you, but it did for me and I was able to add 3 months with no new key provided via email.
So try this at your own risk. perhaps just pay for one month to test it. You can always reclaim payment from Paypal if subs is not renewed.