internet from 100mpbs to 3mbps.

I have business internet to run credit and watching only 1 TV.  The first month running smoothly more than 100mbps.  Since last week it have been slow down from 3mbps down to point (.)15mbps.  Barely able to watch TV and struggle to run credit card.  Call them up and even upgrade and replace 2 different gateway and still crappy speed.  Do we get partially refund or any fix to this before I go back to xfinity?  Tmobile is so unreliable for business and if this doesn't fix soon then how can I recommend to my other business friends?.