assumption of mortgage

hi po. hope u can help me. my husband and i bought a brand new car pero installment. nakapangalan un s brother in law ko kasi he is an ofw so complete ang requirements nya pra maaprove an ng bankfor car loan... bale 4 months n namin nahulugan ung car and we decided na ipasalo ung unit because we've decided to get a different unit. sa madaling sabi nakakuha kmi ng mag aasume ng balance. she gave us the downpayment nahinihingi namin and blank pdc's pra s monthly payment ng unit. ngayon po is tumalbog yung tseke nya. di n namin sya makontak. my pinirmahan kming deed of sale with assumption of mortgage. panu po ang da best gawin? pra mabawi namin ung sasakyab coz we dont know the buyer personally,di narin nin makontak. dpt ba namin iblotter n sya and itimbre s lto ung unit pra mabawi po namin ung sasakyan?. tnx po

pg nakita ung unit pwede ba naminbawiin basta2 ung unit kasi di sya tumupad s usapan namin,nakalagay dun s contract na if she fails to pay the monthly payments of the unit,need nya isauli ung unit thus making the agreement nullandvoid