Tenant not paying agreed upon rent raise

[Ariel Jeidel]

I raised tenant's rent from $4,500 to $5,000. Probably should have sent official notice right away but was a more personal relationship so took 3 months, maybe more, to pin them down as they ignored or didn't show to all my requests for phone call and meeting to discus. I know very large raise but probably could get more on market and my real estate taxes went up about 5k this year, so only really breaking even on this. Tenant was very unhappy and had a whole back and forth. Told them they are welcome to leave and find something cheaper. They went looking and realized they are still quite a bit below market and agreed to stay and pay the $5,000. Not comes the 5th of the month, and they only paid the old rent and are saying they won't pay $5,000 ...

This is NY, poor landlord rules, and don't know how I can get them to pay.

Advise?