Hi PlamenDimitrov
welcome to the Apple (user-to-user) Community.
Re: "Could you please investigate and advise me what is happening"
As we are all Apple users, like yourself, in this Community, we have no access to your accounts or details to check this out for you. We'd like to help, however.
CloudOTP seem to be an authentication service
OTP means "one time password" for logging on to a service
There is a discussion thread on a similar situation in the Community:
Cloudotp - Apple Community
It contains an answer from a community Specialist : nbotros
who says:
"We understand the concern with this situation, and we'd like to clear things up. If you don't recall signing up or subscribing to this service, maybe someone else entered their phone number incorrectly, and it matches yours when they tried to sign up for this service.
With that being said, you can use the tips in the following link to block these unwanted messages:
Block, filter, and report messages on iPhone
We hope this information is useful".
So hope this helps you!
All the best :-)