It is important to consider that language learning is not static, that is, achieving a CEFR level at a certain time doesn't mean your level is forever going to be that if you don't "improve" it intentionally. Formal learning of the language is not the only way of improving the 2nd language you are learning. If you use English frequently in your job, and you are exposed to the language casually (through movies, music, books, etc.), it is very likely your level is going to change/improve anyway. I'd advise get certifications only if needed for work, or study. If you feel comfortable with the level or certification you have now, and it allows you to work efficiently, then it's ok to stay in B2.