If your card is really duff, you can do the following.
Ring up Navionics.
Tell them you suspect your card has gone duff.
They will charge you (several hundred of your pounds) and then post you a new card (and an UP-TO-DATE NEW ONE at that!).
You send your card back to them.
They examine it (or probably not, as I NEVER checked my returns-too expensive to check each return and too cheap to replace anyway), confirm its duff (cough, cough) and re-credit you with the whole amount.
This way you pay for the postage but end up with an up-to-date card.
"Ribbing-the most expensive way of traveling third class"