You are currently in a serial refusals situation. The first answer for this type of situation is "stop applying"! While this advice seems merely pedantic, serial refusals indicate a fundamental misunderstanding of how the process works and what they want to see.
If I can get a Schengen visa, would that help me with my future UK
visa applications ?
Yes. All evidence of peripatetic activities in the affluent countries of Europe and North America is massively helpful. "Helpful" means it adds credibility to the applicant's premise; it is not, however, a guarantee of success.
Another question: In my second UK visa application, the officer sad
that I requested 45 days, but I only requested 4 days, Is there any
channel or a way to get clarifications ?
Generally no. They will never reverse a decision once it has been made. They might, however, be willing to issue you an edited version of your refusal notice that corrects the typo.
How long is the recommended cooling off period in this type of
There is no cooling-off period for a UK refusal, you can make a fresh application on the same day they return your passport. Moreover, there is no "recommended" amount of elapsed time and anyone saying differently is just internet babble spewing out recklessly uninformed pap.
What's important is to stop thinking in terms of cooling off periods and instead think in terms of personal circumstances and how these can be changed. It means if you wait 6 months or a year and still have the same job, the same lifestyle, the same cash flows, same homeland connections, and the same everything else, you will get refused again. To improve your chances of success, you should seek a root-level change in your social, economic, and lifestyle conditions; these are the things they will be looking for.
Professional advice from a member of the UK Law Society with a practice area in visitor visas may be able to help you present your personal circumstances in a more favourable light, but those people earn fees for their work and so it depends upon your own appetite for mobility.
I want to clarify things so these refusals won't affect my future
Clarifications and explanations go into a fresh application; it's the only way they will acknowledge something. That's why it's important to get professional help so that your pattern of serial refusals is fixed.
Thank you for you answer. Can i send a review request and say that I
want only to get clarifications and not appeal ?
Once again the answer is 'no', and firmly so. You can always send them something or even make a formal complaint to Marsham Street, but all you will get is a form letter from the correspondence unit advising you to make a fresh application.
Note: after this answer was posted, you modified your question to include scans of your refusal notice. Once again thanks for observing site courtesy. Your refusal is on grounds V 4.2 a+c. This is a very common, garden-variety refusal and there's nothing special about yours either positive or negative. Our recommended next step for you is to carefully read UK visa refusal on V 4.2 a + c (and sometimes 'e') and consider instructing a UK solicitor.