You are far beyond the time to appeal the court's judgment. You are pretty much stuck with it. Talk to an attorney with all facts and paperwork to verify this. If you can offer the creditor an immediate lump sum payment of 50%, it might be accepted.
You wrote, "[In] looking back at the contract I noticed that they added on a service contract that I did not request or agree to by way of initialling the contract."
Initialing a contract is used for amendments meant to change the written/printed text of the contract. The initialization of the contractual terms are finalized by the subscription of the signature.
If you signed the contract, you are likely bound under law.
Courts can only issue garnishments after it has entered judgement and the time for appeal has expired.
The Court rules do not allow a party to use the garnishment objection process as a way to "appeal" or "overturn" an otherwise valid judgment. The only thing at issue in the garnishment process is whether the funds that the creditor is seeking to attach are somehow exempt from attachment.
If you want to try to overturn your judgment. You will need the help of an attorney.