Hey Matthew -
This sounds like a very unusual problem combined with some amount of confusion. I will do my best to break it down here -
Our free trial is for 50km OR 14 days, whichever occurs first. When you say it has been recorded against your account, does that mean you have a successful payment to Zwift via your PayPal? It sounds as though you have exhausted your free trial and are now a subscriber - otherwise you would not be able to ride at all after finishing your free trial.
The issues occurring to you in game are unrelated to your payments. You said you can ride a few hundred meters before everything resets - can you please clarify for me what you see when that happens?
Is it the numbers in the blue box in the upper left of the screen that reset, or the numbers in the white box at the top, or both? Do the numbers show ‘0’ when they drop, or do they look grey and show ’ - - '? How long of a pause is there before you are able to continue riding? What type of equipment are you using in your setup?