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I am sorry to hear about this situation. Someone in your situation is a tenant at sufferance, meaning you live on the property at the discretion of the landlord but without paying rent (the fact that you have paid utilities does not affect this). See Florida Statutes 83.04.
There is no set days for notice to quit for a tenant at sufferance in FL, but standard is 60 days, not 90. If you provide me with the your source of 90 days, I can comment on this.
Someone in your situation may wish to write back a formal letter, demanding a WRITTEN NOTICE TO QUIT. Otherwise, the new owner cannot begin eviction prior to a formal notice being sent. This may buy you some time.
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