First of all, according to the information provided, if you owe 14,000 yuan to your China Merchants Bank credit card in 2012 and have not repaid it for more than 3 months, the bank will require you to repay it through collection methods. If you still owe about 800 yuan as of April, and you received a call from a Guangdong law firm in May urging you to sue, then you may face the risk of prosecution.

The specific instructions are as follows:

1. Amount and time limit of debt owed: You owe 14,000 yuan to your China Merchants Bank credit card and have not repaid it for more than 3 months, which is considered an overdue repayment. According to the credit card contract and relevant legal provisions, banks have the right to take legal measures to recover arrears.

2. Collection process: The bank uses collection measures to require repayment from you. It will usually contact you through phone calls, text messages, letters, etc. to urge you to pay off the debt.

3. Lawyer lawsuit: If you owe a large amount and have not repaid it for a long time, the bank may entrust a law firm to file a lawsuit. Receiving a call from a law firm notifying you of a lawsuit means that the bank has taken legal proceedings and may take further legal action against you.

Summary:

According to the information provided, if you owe 14,000 yuan to a China Merchants Bank credit card and have not repaid it for more than 3 months, you may face the risk of being sued. Banks usually pursue collection measures to recover arrears, while lawyer prosecution is a possible measure when overdue situations are serious.

Extended information:

1. Overdue repayment of personal credit cards will have a negative impact on personal credit records and credit scores, and may affect personal financial behaviors such as future loans and credit card applications.

2. When faced with overdue debt, it is recommended to contact the bank or relevant institutions in a timely manner and proactively seek a repayment agreement or seek legal advice to reduce possible legal risks and consequences.

The above answers are for reference only. Please consult a professional lawyer or relevant legal institution for specific circumstances.