Unfortunately the seller assigned incorrect plan working for hot spots only, which doesn't allow to make calls.
Next day I visited the store again, wasted another hour there just to know "we cannot fix it today, it is too late, assistance is shutdown", you have to visit us again. Next day I tried to call the store - got busy line, tried to call a guy from the business card they gave - no luck, left a message - nobody called back. Then I called AT&T prepaid customer service, however they said I have to visit the store, only the store where the line was bought can change the plan. I could not believe my ears that it may happen for a company like AT&T in 21 century. I asked to involve the manager, the manager tried to call the store, but she also could not reach them, they just switched to each other and didn't intend to cooperate (this is what she told me), so she finally said I have to visit the store. If one expected customer support can change the plan, or they can send an email to the person who can do that, or open an internal service request in order to have it done - that would work in another company, but not in AT&T. With AT&T I have to visit the store where the plan was bought again to change the incorrectly assigned plan.
Unfortunately that store is too far from me (well the ones closer to me are even worse) I don't have time to drive there again and again and waste hours there. Finally I used all possible options, all didn't work, I still have and pay for two plans not allowed to make or accept calls.
What can be done to have AT&T customer support? Some managers probably should try their talents somewhere in another areas.