It appears that the supplier may have breached their supply of services contract with you. The supplier is under a duty in contract law and statute to provide you with a product and service that is fit for purpose, of reasonably satisfactory quality and matched the description at the point of sale. Your damages will be a refund on the price paid for the period when their services were not up to standard, plus additional costs of rectifying their defective work through another supplier.
You have not yet terminated the contract for actual and/or repudiatory and/or material breach of the contract. There is a risk that a court will consider that you have “waived” the breaches and permitted the supplier to continue the performance of the contract by implication of your inaction. You will be unable to terminate the contract for historic breaches if you later change your mind and decide to drop the supplier. The court will take the view that you ought to have “accepted” the supplier’s breaches and terminated the contract as soon as reasonably practicable after discovering the breaches.
You must serve a written “final warning” against the supplier putting them on notice that you are dissatisfied with their services, that they are potentially in breach of the contract and they must improve their services and rectify any defects in their performance of the contract and the goods and services that they are providing within a reasonable period. A “warning period” of between 28 days and three months is more than reasonable, depending on the nature of the contract.
Once you have terminated the contract and find that you are “out of pocket” in respect of fees paid for goods and services purchased but not received, whether to the required standard or at all, you must then present a civil claim for damages against the supplier.
If your expected damages are under £10,000, you may issue court proceedings via the Government’s Small Claims Track Online System: https://www.gov.uk/make-money-claim. The issue fee will be no more than £410.00. A party cannot normally recover solicitors’ costs on the Small Claims Track. However, it is designed for non-lawyers (known as “Litigants In Person”). The trials are relatively informal, and the judges do not expect parties to have the same legal knowledge as experienced solicitors and barristers.
Before you issue Court Proceedings against them, you should send a letter of claim to them. There are plenty of free templates online and the consumer protection advice magazine/website “Which?” has a useful template which you can adapt to your claim: https://www.which.co.uk/consumer-rights/letter/letter-before-small-claims-court-claim.
However, if your expected damages are between £10,000 and £25,000, the claim will be allocated to the Fast Track, and if damages are over £25,000, it will be allocated to the Multi Track. These tracks are much more formal and legally technical, and it is expected that both parties will instruct solicitors. The normal rule on the Fast and Multi Tracks is that the winning party (either at a Final Hearing, or through a negotiated settlement) can expect to receive most of their legal costs from the losing party.
If your claim is worth over £10,000, I strongly recommend that you instruct specialist commercial dispute resolution and court litigation solicitors to advise you and conduct the litigation. If you cannot afford legal costs upfront, you should contact your home or business insurers and ask if they will cover your legal costs under a legal expenses insurance policy. They will either pay your solicitors’ fees or appoint a law firm on their panel of solicitors to act for you.