score:4
Is there any limit on how much time can pass before receiving a refund?
Irrelevant question. Most airlines happily ignore what EU 261 says because the enforcement is weak. Assuming that you did NOT accept a voucher, you are clearly entitled for a full refund. It's also clear that Level has no intention of paying and just hoping you will go away on your own (which unfortunately is common these days).
You've already been contacting them regularly but apparently the "squeaky wheel" approach doesn't work here. Some options: