Welcome to T-Mobile! It sounds like has been bumpy start coverage-wise. Thanks for providing all the initial info that I need to take a look at the area. From checking out our tower locations in comparison to your office building, you should have no issues picking up a strong signal. If you're by a window, does your signal strength increase? I see a few taller buildings in the area but that shouldn't decrease your signal. Do you know of any other T-Mobile users at your work that have the same complaint? The next step we need to take is working with our Tech team via 611 or T-Force via Facebook/Twitter to have a ticket filed with our Engineering team. They'll investigate the area within 72 business hours.
To answer your last question, you are still within your Buyer's Remorse period if you activated service on 8/12. If you started up service in a store, you have 14 days. If started online or over the phone, you have 20 days from the date you receive your phone.