Lost Annual Oyster Card

That's not quite right. Can I ask which Visitor Centre you went to? Some have fabulous staff who know the TOM inside out, others are a little lacking (not entirely unforgivable, as it's not their core business).

Was the card you used a new card, or had it previously been used (and perhaps refunded?)?

Code 70 can mean two things, so it's important to establish if it's happened more than once, or if it was a one-off (and you didn't 'try again'). Another clue would be what a POM displays when the card is presented.

Basically, if the card is faulty any* tube station can change it over for you, without a problem. If you transferred it to an old/used card, they can still transfer it but it would be entirely discretionary, and would require a little more time to complete. You'll also need ID to verify the registration details of the Oyster card. If it's a brand new card, and isn't faulty, unfortunately only the helpline (Via phone) will be able to help, and it will probably mean that you need to buy a new card.

*Every Tube station has the capability, but whether they are able to is another thing entirely. Small stations tend to now be single-manned and probably won't be able to help; you're best trying a gateway station where more success has been reported.

I bought a new card that had to be used once before I could register it online. When I sign in to my Oyster account I can't even see the Oyster that I transferred my Oyster onto.