I would contact your cell phone carrier and request their assistance. You might want to speak to the tech-support unit rather than merely customer service. Keep a log of your calls to them and their response.
It may be necessary to write them a written complaint. Use postal certified mail with receipt, not email; this way you have a hard record. Certified letters -- which they have to sign for -- tend to get more attention.
Earlier in this newsgroup it was reported that mass market calls were originating out of VOIP lines and giving nonsensical caller id numbers like 111-111-1111. (I got such marketing calls during the political campaign -- the Dems were so desperate they called repeatedly all day long with recorded pitches. It was a nightmare.) Anyway, maybe hackers on VOIP are able to slur callerID. It's strange that a number
555-1212 would be used since that's directory assistance, and I can't help but wonder the originator purposely set that number up to be seen. That is troubling.