Accepting Partial Payment During Foreclosure Process

Hey all, looking for some assistance. My dad has a second trust deed on a SFR in Lemon Grove, CA. He filed Notice of Default. Prior to the Trustee Sale, he agreed with borrower to extend the trustee sale if the borrower paid my dad $3K. This was memorialized with an email exchange. This was to give borrower time to sell home. They did this for 4 additional months. My dad would send him an email asking for another $3K to postpone the sale.

Now borrower has a lawyer that is saying that because my dad accepted these partial payments (without a formal forebearance plan), he has invalidated foreclosure process and the process needs to start over at 0.

I have a call into my attorney friend but I would assume people on this board have a lot of experience in this area. Thanks in advance for the assistance.