I received an email of successful submission and ID of manuscript. After 2 months when I follow up they said that they could not find the manuscript. Should I just submite to another journal ?
First, you have to attach the successful submission and ID in an email to the journal if they reply the same you need to have confirmation from them that your manuscript is not under process for publication. If they confirmed, you can go ahead and submit it to another journal.
I'm telling you about the confirmation to avoid any kind of issue with the second journal, with that serial of emails you will be on the safe side.