Strengthening micro USB connector
The first thing I would do on future boards, is to add 3-4 vias around each of the ground pads of the connector, connected to the pads wia a plane. Then make sure to have a plane area on the bottom of the board as well connecting the vias together.
These extra vias act as an anchor which ties the ground pads through the board giving them significantly higher strength. Place two on the inside of the pads, and two on the outside of the pads.
Secondly, during assembly you could instruct your assembly house to bond the connector to the board with Epoxy (e.g. the red dots you see in the second image). They should already be set up for this as they deal with double-sided circuit boards and tall surface mount components like capacitors.
As a third option, you could use a different USB connector. Some have little plastic pegs underneath them which act as alignment pegs but also provide some strength to resist the connector being pushed backwards. Alternatively a mixed-technology connector which are surface mount style but have through-hole ground pins for added strength.