Tried to change sim...didn't work...both sims now invalid...I have a balance on this account...need some help!
What do you mean your SIM is invalid? If your account expired, you can't have just topped up - has your base plan expired? Can you still log into self service and what does it say there? If your account still exists, all you need to do is renew your base plan to resume service that's why I'm puzzled what you mean exactly.
Wait, I now see you added to your message, sorry I missed that. It could be that the second SIM was faulty, that in itself is no problem. All you need to do is exchange it for another one, activate that in self service and you're good to go again. I've had it happen too, it's a pain but no permanent harm done - your account, number and balance are quite safe :)