Marketing messages need consent in most jurisdictions, and consent means a person actively agreed — not that they bought something once and their number ended up in a spreadsheet.
Record where each number came from and when. An imported list with no provenance is the one that generates complaints, and a complaint against your own SIM is a problem for your own number rather than for a provider's shared pool.
Honour opt-outs permanently, and keep the record of the opt-out rather than deleting the contact. A deleted contact comes straight back on the next import; an unsubscribed one does not.