a former tenant of mine refuses to honor our contract and claims it is null and void since it is not notarized what should i do?

i had a problem with a tenants smoking pot in a house i own. after receiving complaints from one tenant that others were smoking on my property i sent all of them an email to inform them that illigal substances would not be on premises. a few months later i caught one tenant smoking in the house and told them they were evicted due to breach of contract. the contract clearly states that if they breach it they must continue to pay rent and utility services untill i find a new tenant. today i received a voice mail from said tenants mother stating that my contract was null and void because it was not notarized and if i attempt to collect rent from her daughter i will be charged with sexual harassment (which took me aback since i only spoke to the tenant when i collected rent and bills). the tenants mother is alsoharrasing my other tenants in what i beleive is an attempt to intimidate me out of pursuing payment. would i be better off cutting my losses or persuing this in court?