I am working currently but in the past i have worked at an insurance firm and at a automobile firm. However, the insurance internship was supposed to be for 6 months and i quit after 4 months. The firm told me that it doesnt issue certificates for internships and i just have one pay slip and the others i have misplaced. I have written this on my cv. The second was an informal internship in the marketing department under a regional marketing head that my uncle knows for 2 months. I have a letter certifying that i worked at aston martin under that guy but i have never attached it. Is it possible that the hr contacts these firms and i dont show up and hence they just dont interview mw further and black list me cause they think i am lying? What should i do?

This varies from country to country. Oral references are really powerful because written accounts rarely give a balanced description of a candidate. If those internships are most valuable thing on your résumé, HR might want to validate them.

is it a problem if the job that i worked for was specific like working in the net promoter score team in the marketing department while i wrote "marketing intern" on my CV?

This varies from country to country. Oral references are really powerful because written accounts rarely give a balanced description of a candidate. If those internships are most valuable thing on your résumé, HR might want to validate them.

This varies from country to country. Oral references are really powerful because written accounts rarely give a balanced description of a candidate. If those internships are most valuable thing on your résumé, HR might want to validate them.

is it a problem if the job that i worked for was specific like working in the net promoter score team in the marketing department while i wrote "marketing intern" on my CV?
It would be a problem if you misrepresented the position or your responsibilities in your CV.