1) your father ought to have executed registered sale deed in your favour
2) will takes effect only on death of testator
3) your father can during his lifetime sell the property inspite of will or GPA executed by him .
4)in order to confer clear and marketable title to the property your agreement ought to have been registered
5)you can move court and seek stay of sale on grounds that by agreement for sale entered into februray 2014 you had paid your father full consideration of the flat . your father had acknowledged receipt of payment and delivered possession to you
6) only sale deed remained to be executed and your father on account of ill health could not do so
7)you can file case of cheating , criminal breach of trust against your father
8) you can refuse to vacate the house
9) don't create any third party rights on the house