If you still have service to your phone, it's unlikely to be a SIM swap attack. Generally, one of the consequences of a SIM swap is that all the services provisioned on your phone (including your phone number) are transferred to the attacker's phone, by the exact same process as those services would be transferred to your new phone when you upgrade. This is the whole point of a SIM swap, because the attacker is trying to intercept any calls or texts which are generated by a multifactor authentication (MFA) scheme to use to impersonate you to that service. More at https://en.wikipedia.org/wiki/SIM_swap_scam.
It's possible, but highly unlikely (unless you are a high-value target of a nation-state-level threat -- and you would know if that were the case), that your SIM could be cloned rather than swapped. Cloning is illegal in the US, and in any case is detectable by carriers who have an incentive to stop such arrangements because they can be used for billing fraud. More at https://en.wikipedia.org/wiki/Phone_cloning.
All of this means that it is likely that it was simply a spoof.