Or Google those terms to find a provider (or email me, for the same result), and buy it yourself (price starts at $110; just expense it later). If they like your degree, you'll get like a 2-3 page wall of text that should usually be sufficient for USCIS. Take that to your lawyers, and make them include it in your application. I'm surprised they didn't get one already for your L-1B.
3 years B.Sc. can definitely be fine, but maybe it depends on the country/university/courses? (In my case it didn't matter; I also have an M.Sc. But they certify what you give them, not just the highest, and so I know my 3 year B.Sc. is ok, at least for the evaluator, don't know about USCIS.). One potential problem is if your subject of study doesn't match exactly (e.g. an EE MSc doing software dev). USCIS has been stricter in those cases in past years afaik.
Also, it's more risky, but x% of a degree + y years progressive experience can sometimes be summed up and then in total considered equivalent to the degree. (Progressive means you can show your job continuously became harder. y years of beginner level wouldn't count. Any work that doesn't directly relate doesn't count either.)
IANAL
(You may have already done this; I couldn't tell from your post. "certificate that proves it does" could refer either to a (useless) piece of paper by your university, or an independent academic equivalence evaluation. So posting this just in case you don't have the latter one yet.)
Lawyers told me that my degree does not qualify as a BSc, even after I send them the certificate that proves it does. Apparently, anything under five years is not considered a BSc. They also told me that my 15+ years of experience have little value, as they will only consider the five most recent.
What is the position of the USCIS about this?