Okla. Stat. tit. 46, § 46-12

In cases where assignments of real estate mortgages are made

after the passage of this act, if such assignments are not recorded,

the mortgagor, his heirs, personal representatives, or assigns, may

pay all matured interest or the principal debt secured thereby,

prior to the recording of such assignment to the mortgagee, or if

any assignment of such mortgage has been made that duly appears of

record, then such payment may be made to the last assignee whose

assignment is recorded in accordance with the provisions of this

act, and such payment shall be effectual to extinguish the debt

secured by such mortgage and all claims against such mortgagor, his

heirs, personal representatives, and assigns, for or on account of

such interest or such principal indebtedness; and no transfer of any

note, bond or other evidence of indebtedness, by endorsement or

otherwise, where such indebtedness is secured by mortgage on real

estate within this state, shall prevent or operate to defeat the

defense of payment of such interest or principal by the mortgagor,

his heirs, personal representatives, or assigns, where such payment

has been made to the mortgagee or to the assignee whose assignment

appears last of record under the provisions of this act: Provided,

however, that in all such cases the assignee who may hold such

unrecorded assignment shall have a right of action against his

assignor to recover the amount of any such payment of interest or

principal made to such assignor as upon an account for money had and

received for the use of such assignee: Provided, this section

applies only to mortgages which have been on record six (6) months

or more.