TAX Sale property can it sell back to the owner?

[Claudia Brown]

Question: 

My ex husband and I owned a property in Pennsylvania.  We bought this house cash to rent, the deed had both his name and mine name. 

after we divorced he kept renting the house and I led him keep the rent money for him to pay the taxes and do with the rest of the money whatever he needed to do for the house.  Two years later I contacted him to inquire about the house and he told me he let the house go tax sale and he bought it back. 

1)  I was never notified about this 

2) How can he re buy the house 

3) I didn't sign anything, can this be done legally?