invalid sim card, how can i be helped

If you're seeing an invalid SIM message, that indicates the phone is carrier locked to a cellular provider other than the one you are trying to use.

Only the carrier it is locked to can unlock it.

Where, exactly, did you get the phone?

What model phone is it?

See if this helps: https://support.apple.com/en-us/HT201407

See this, How to unlock your iPhone for use with a different carrier - Apple Support KiltedTim said to ask your Aunt what carrier the device was using. If she is the original owner, only she can ask the carrier to unlock the iPhone.

If you are just seeing an error that says invalid SIM, and not that the SIM is not supported by the activation, then you need to contact your carrier where you got the SIM.

Then ask her what carrier it's locked to.

Yes. I get that.

As I said, that's because it is locked to a cellular carrier other than the one you are attempting to use.

Let me ask an additional question. First you say invalid SIM card, then you say the activation server cannot be reached. Can you please provide the entire exact error message? It could mean more than one thing.