Is it a prepaid plan? If so add funds to your account.

No tengo la sim y no me se el número 

Do you mean, you updated your iPhone and the SIM all of a sudden became locked to T-Mobile?  If so.  Wherever you got it from used a hack that was patched in the update that circumvented the SIM lock on the device.  For a device to be eligible for a SIM unlock from T-Mobile.  You must be a T-Mobile USA customer and your account and device must meet all of the SIM Unlock Policy requirements.  

SIM Unlock Policy | Unlock Your Mobile Wireless Device | T-Mobile