Tier 2 General Absence details

Hi All,

Please can someone help with guidance:
I moved to the UK on 17/08/2017 through a Tier2 General visa and switched to another employer(Y) on 15/05/2019. However, my first employer(X) didn't pay taxes for the first year, paid £1300 for the second year (I do not have any clue that on what basis that the tax paid where my annual salary was 45k)

2) When I was working for my first employer(X), I was out of UK during the following Periods, and I'm not sure whether he submitted to HMRC as paid leave/unpaid leave.
27/04/2018 to 13/05/2018
11/07/2018 to 23/07/2018

With that, can you guide how to submit details of absence with the above criteria?

Thanks,
Abhi