Check this:

http://www.mtt.ru/info/def/index.wbp?def=919&number=6575267

This number belongs to a Russian mobile phone operator "MTS" (subregion of the Republic of Chuvashia).

The reason why you are getting these messages is less obvious to me, but I guess it *might* be a bug in the billing system or someone's faulty phone tracking system.

I might ask someone to clear this up if you wish, but I'm not sure that they will be able / willing to do so.