A: With cracks in the frame it sounds like--regardless of the fuel injectors or transmission--the car is unsafe to drive. You should find competent mechanics and follow their advice. Under the facts as represented your vehicle must have been out of service for prolonged periods and, if under warranty, the manufacturer should have offered a buyback. If it hasn't, you should contact a competent consumer attorney as soon as possible.
Money should not prevent access to justice. The state legislature understood that the average consumer cannot afford to hire their own attorney and enacted consumer protection laws that provide fee shifting. This means that if you win your case, the dealer or manufacturer defendant must pay your attorneys' fees.
A: Sorry to hear about your problem in getting your money back. You should consult with a consumer law attorney and possibly law enforcement as soon as possible. You haven't included much information here, but this could be a problem with the company, the third party selling you the car, or with a scammer. You will want to take action as soon as possible.
A: Sorry to hear about your trouble with this company. There seems to be a lot going on here and asking questions online is no substitute for consulting with an attorney.
To answer the narrow question, it is not legal to be charged more than you authorized for the purchase. If this company cannot explain the additional charge and will not cancel the transaction, you may contact your credit card company to reverse the charges.
Good luck with resolving the matter,