can not access bitcoin in an address that belongs to a discontinued wallet, although i have the 12 word phrase?
If you have a 12 word recovery phrase for the old wallet, if the phrase is a BIP-39 recovery phrase and if you can find the derivation path, you should be able to recover control over your money using a standalone wallet that supports BIP-39 and which allows you to specify the derivation path.
You could use a list of popular derivation paths as a starting point for your own larger list and systematically work through them.
It would be easier if the original business could tell you the derivation path used in their discontinued wallet.