What kind of card/account do you have?
For example, my wife opened a bank account and was immediately issued a Visa debit card with logo and everything, that can be used at stores, at least in Argentina. We thought it would also work for things like online purchases, but we were wrong, not even in Argentina, like at Mercado Libre.
It had the visa logo, but the expiration date was like 2021 or 2030 or something, I don't remember. It was never accepted for anything other than store purchases.
It wasn't until a year on the account (I think - maybe it was 6 months?) that she was issued a credit card, an Amex. That works like a credit card and we could use it online, etc.
This was all on a caja de ahorro, which is what most of us expats, at least, will have to start out with; or maybe a special account the company someone works for sets up to deposit salaries for the workers every month. I don't much about the latter, if it's a caja de ahorro or something special, so I can't comment on that.
After 18 months of perfect usage - no negative balances, payment on time or ahead on zero-interest loans made at stores and payment of the Amex balance every month (we never rolled it over into payments although option is available at a high interest rate) - the bank set her up finally with a checking account, with a checkbook and everything.
As well as a real debit card, a Visa. Looks pretty much like a debit card from the States (which the other one didn't, quite), with the logo and a proper expiration date. That card works.
I don't know if this fits your situation, but if so, that's why it won't work. Forgive me if I'm telling you something you already know and it's an Argentina banking thing